I've got a 1927a1 that I'd like to make another bolt for. It's .45 ACP,
and strictly a blowback mechanism. Any hints on which alloy of steel to
use, and/or what hardness to "shoot" for when heat treating? Seems
pretty soft as shipped and the grinder test doesn't seem to tell me
there's a whole lot of carbon, but it's been a long time since I've had
someone teach mhow to read sparks to guess at alloy.

Thanks
Dave

Ask on the gunbroker.com forums lots of gunsmiths post there including
me and somone would surely know. Theres probably quite a few choices
for what you could use as for hardness I don't know off hand I could
probably find out but it would take time, which I currently don't have.
Sorry.

P.S. have you thought about just buying a new bolt? Would probably be
cheeper time wise in the longrun.

"Dave Hinz" wrote in message
...
I've got a 1927a1 that I'd like to make another bolt for. It's .45 ACP,
and strictly a blowback mechanism. Any hints on which alloy of steel to
use, and/or what hardness to "shoot" for when heat treating? Seems
pretty soft as shipped and the grinder test doesn't seem to tell me
there's a whole lot of carbon, but it's been a long time since I've had
someone teach mhow to read sparks to guess at alloy.

Thanks
Dave


Don't know if this is any help but Hatcher's Notebook shows a M1 Garand bolt
of 8620 treated to Rockwell C 55 to 59 and the M1 Carbine bolt of 4140
treated to Rockwell C 48-54. I thought I remembered Thompson info in the
book also but was incorrect.

Steve.

On 17 Mar 2006 01:14:37 -0800, redice wrote:
Ask on the gunbroker.com forums lots of gunsmiths post there including
me and somone would surely know. Theres probably quite a few choices
for what you could use as for hardness I don't know off hand I could
probably find out but it would take time, which I currently don't have.

I'll take a look over there, thanks.

P.S. have you thought about just buying a new bolt? Would probably be
cheeper time wise in the longrun.

Well, cheaper isn't the point. It's a fairly complex part, and I'd
like to test my skills by making one. By using something that's easy to
test, I can spend some quality shop time and make something useful in
the process. The finish quality on the Kahr manufactured bolts is not
very good, and I'm hoping to improve on that as well.

Thanks,
Dave

On Fri, 17 Mar 2006 10:06:39 -0500, SteveF wrote:

Don't know if this is any help but Hatcher's Notebook shows a M1 Garand bolt
of 8620 treated to Rockwell C 55 to 59 and the M1 Carbine bolt of 4140
treated to Rockwell C 48-54.

Ah. Of the two, the carbine's is probably more relevant - I'm not
locking any lugs into anywhere, And, I have 4140, so it's a good
starting point. Thank you.

I thought I remembered Thompson info in the
book also but was incorrect.

Yes, I thought he wrote something about it also. I've got I think all
of his books, so it may take some digging.

Dave

On 17 Mar 2006 16:51:35 GMT, Dave Hinz wrote:

On Fri, 17 Mar 2006 10:06:39 -0500, SteveF wrote:

Don't know if this is any help but Hatcher's Notebook shows a M1 Garand bolt
of 8620 treated to Rockwell C 55 to 59 and the M1 Carbine bolt of 4140
treated to Rockwell C 48-54.

Ah. Of the two, the carbine's is probably more relevant - I'm not
locking any lugs into anywhere, And, I have 4140, so it's a good
starting point. Thank you.

I thought I remembered Thompson info in the
book also but was incorrect.

Yes, I thought he wrote something about it also. I've got I think all
of his books, so it may take some digging.

Dave

I think you would be golden with 4140

Gunner


"The importance of morality is that people behave themselves even if
nobody's watching. There are not enough cops and laws to replace
personal morality as a means to produce a civilized society. Indeed,
the police and criminal justice system are the last desperate line of
defense for a civilized society. Unfortunately, too many of us see
police, laws and the criminal justice system as society's first line
of defense." --Walter Williams

On Fri, 17 Mar 2006 17:42:36 GMT, Gunner wrote:
On 17 Mar 2006 16:51:35 GMT, Dave Hinz wrote:

Ah. Of the two, the carbine's is probably more relevant - I'm not
locking any lugs into anywhere, And, I have 4140, so it's a good
starting point. Thank you.

I think you would be golden with 4140

Good to hear. Any thoughts on where I should shoot for on the
hardening?

Dave

Have you developed your methodology?

In my recollection, the 1927A1 bolt is a bar stock part , rectangular in
cross section with a round turned projection in the front about 2~3" long
that accomodates the ctg head at the end.

If you heat treat after machining you will be susceptible to warping,
dimensional change, and scaling of your machined surfaces.

So, are you planning on surface , slot, & cylindrical grinding after HT?

I don't believe the factory bolt was heat treated, really no need for it.
It's an unstressed part for a low pressure ctg. I also believe the extractor
is staked in place, furthering the need for metal that is suitable for
deformation.

I think any un-heat-treated steel available from 1018 to 4140 would fit the
bill.

Tony


"Dave Hinz" wrote in message
...
On Fri, 17 Mar 2006 17:42:36 GMT, Gunner
wrote:
On 17 Mar 2006 16:51:35 GMT, Dave Hinz wrote:

Ah. Of the two, the carbine's is probably more relevant - I'm not
locking any lugs into anywhere, And, I have 4140, so it's a good
starting point. Thank you.

I think you would be golden with 4140

Good to hear. Any thoughts on where I should shoot for on the
hardening?

Dave

On 17 Mar 2006 18:16:42 GMT, Dave Hinz wrote:

On Fri, 17 Mar 2006 17:42:36 GMT, Gunner wrote:
On 17 Mar 2006 16:51:35 GMT, Dave Hinz wrote:

Ah. Of the two, the carbine's is probably more relevant - I'm not
locking any lugs into anywhere, And, I have 4140, so it's a good
starting point. Thank you.

I think you would be golden with 4140

Good to hear. Any thoughts on where I should shoot for on the
hardening?

Dave


50-52//just as a gut feeling.

Is the sear carried on the bolt?

Gunner


"The importance of morality is that people behave themselves even if
nobody's watching. There are not enough cops and laws to replace
personal morality as a means to produce a civilized society. Indeed,
the police and criminal justice system are the last desperate line of
defense for a civilized society. Unfortunately, too many of us see
police, laws and the criminal justice system as society's first line
of defense." --Walter Williams

On Fri, 17 Mar 2006 20:27:02 -0500, Tony wrote:
Have you developed your methodology?

In my recollection, the 1927A1 bolt is a bar stock part , rectangular in
cross section with a round turned projection in the front about 2~3" long
that accomodates the ctg head at the end.

Yes.

If you heat treat after machining you will be susceptible to warping,
dimensional change, and scaling of your machined surfaces.

So, are you planning on surface , slot, & cylindrical grinding after HT?

Looking at it further, I was considering making the cylindrical part
seperate, and inserting it into the rectangular part with a
low-clearance fit and pins.

I don't believe the factory bolt was heat treated, really no need for it.
It's an unstressed part for a low pressure ctg. I also believe the extractor
is staked in place, furthering the need for metal that is suitable for
deformation.

In the current production at least, the extractor is held by it's own
spring tension into a t-slot milled into the bolt. I'm trying to think
where I've seen another like it but can't think of one offhand. But to
remove the extractor from the bolt, you merely lift it "outwards" with
the head of a cartridge and pull it forward. It doesn't come out in use
because the outward motion is constrained by either the receiver, and/or
the spring tension of the extractor itself.

I think any un-heat-treated steel available from 1018 to 4140 would fit the
bill.

Any thoughts about the 2-piece fabrication idea? Or, of I won't be heat
treating, then really could just do my offset with the 4-jaw; everything
else other than that extractor slot is pretty straightforward.

Thanks,
Dave

On Sat, 18 Mar 2006 10:57:29 GMT, Gunner wrote:
On 17 Mar 2006 18:16:42 GMT, Dave Hinz wrote:

(4140)

Any thoughts on where I should shoot for on the
hardening?

50-52//just as a gut feeling.
Is the sear carried on the bolt?

No, but of course that leads to the followup question. The firing pin
on the 1927a1 rides with the bolt, and is a piece of 1/8" flatstock cut to
an interesting contour. I made a new one (broke the firing pin tip off
of the original one due to my sear spring reduction experiments).
However, after only a few hundred rounds, the firing pin where it mates
with the sear, is showing rounding. It's unknown alloy. An point in
trying to harden that, at least in the part which meets the sear? I'm
completely ignorant of heat treating, which is pretty obvious at this
point, but I'm thinking get that local area of the firing pin up to
cherry red or so, and quench in oil?

Without knowing the alloy, I know it's a crapshoot. But knowing the
person I got these materials from, if it's newer than 1970 technology
I'd be shocked. Any thoughts?

The firing pin is a piece of flat stock affair with the tip slightly rounded
where it strikes the primer. I would use mild flat stock & case harden for
45min~1 hour in Kas-en-it @ 1600d F. You will need to harden the part since
it is subject to high wear, especially where the sear catches.Since this
part is relatively simple, you can straighten out any warpage that occurs.
And the soft core will reduce the possiblilty of a sudden failure during
usage, an important feature in any firearm ignition system.

Of course you can get any of these parts from GPC or other sources, but that
might not be as fun.

Tony


"Dave Hinz" wrote in message
...
On Sat, 18 Mar 2006 10:57:29 GMT, Gunner
wrote:
On 17 Mar 2006 18:16:42 GMT, Dave Hinz wrote:

(4140)

Any thoughts on where I should shoot for on the
hardening?

50-52//just as a gut feeling.
Is the sear carried on the bolt?

No, but of course that leads to the followup question. The firing pin
on the 1927a1 rides with the bolt, and is a piece of 1/8" flatstock cut to
an interesting contour. I made a new one (broke the firing pin tip off
of the original one due to my sear spring reduction experiments).
However, after only a few hundred rounds, the firing pin where it mates
with the sear, is showing rounding. It's unknown alloy. An point in
trying to harden that, at least in the part which meets the sear? I'm
completely ignorant of heat treating, which is pretty obvious at this
point, but I'm thinking get that local area of the firing pin up to
cherry red or so, and quench in oil?

Without knowing the alloy, I know it's a crapshoot. But knowing the
person I got these materials from, if it's newer than 1970 technology
I'd be shocked. Any thoughts?

On 18 Mar 2006 18:13:41 GMT, Dave Hinz wrote:

On Sat, 18 Mar 2006 10:57:29 GMT, Gunner wrote:
On 17 Mar 2006 18:16:42 GMT, Dave Hinz wrote:

(4140)

Any thoughts on where I should shoot for on the
hardening?

50-52//just as a gut feeling.
Is the sear carried on the bolt?

No, but of course that leads to the followup question. The firing pin
on the 1927a1 rides with the bolt, and is a piece of 1/8" flatstock cut to
an interesting contour. I made a new one (broke the firing pin tip off
of the original one due to my sear spring reduction experiments).
However, after only a few hundred rounds, the firing pin where it mates
with the sear, is showing rounding. It's unknown alloy. An point in
trying to harden that, at least in the part which meets the sear? I'm
completely ignorant of heat treating, which is pretty obvious at this
point, but I'm thinking get that local area of the firing pin up to
cherry red or so, and quench in oil?

Without knowing the alloy, I know it's a crapshoot. But knowing the
person I got these materials from, if it's newer than 1970 technology
I'd be shocked. Any thoughts?


Dont bother with Mystery Metal. Get a piece of O1 or similar and make
a firing pin. If you need one..Ill dig though the stacks.

Btw...as I recall..the Thompson was never meant to have a light
trigger. You yank it, not squeeze it.

Gunner



"A prudent man foresees the difficulties ahead and prepares for them;
the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3

On Sun, 19 Mar 2006 05:28:47 GMT, Gunner wrote:
On 18 Mar 2006 18:13:41 GMT, Dave Hinz wrote:

Without knowing the alloy, I know it's a crapshoot. But knowing the
person I got these materials from, if it's newer than 1970 technology
I'd be shocked. Any thoughts?

Dont bother with Mystery Metal. Get a piece of O1 or similar and make
a firing pin. If you need one..Ill dig though the stacks.

Yup. I came to that conclusion over the weekend myself. I don't owe
this metal anything, and if I don't know what it is, or how it behaves,
spending an afternoon on something complex only to have it be unusable
(the bolt, not the firing pin) would be silly, when known material is
readily available. Relative values and all that.

So what do I do with this accumulation of unknown steel then? And, more
importantly, why am I asking _you_? (written with a smile, I assure
you)

Btw...as I recall..the Thompson was never meant to have a light
trigger. You yank it, not squeeze it.

can't/won't train myself to do that to a trigger. It's reasonable as
reworked which is as good as I can expect to get. I learned enough
making the first pin out of "mystery metal" that I now know how to jig
it, which order of operations, and so on. So I'll get some of the right
stuff and make one just like it but better. (and save this one as a
spare, because it does work).

I'll post some pics if there's anything picworthy.

You can often greatly improve a triggerpull safely by limiting overtravel.
A small allen cap screw from behind the trigger guard will serve nicely.

Tony

"Dave Hinz" wrote in message
...
On Sun, 19 Mar 2006 05:28:47 GMT, Gunner wrote:
On 18 Mar 2006 18:13:41 GMT, Dave Hinz wrote:

Without knowing the alloy, I know it's a crapshoot. But knowing the
person I got these materials from, if it's newer than 1970 technology
I'd be shocked. Any thoughts?

Dont bother with Mystery Metal. Get a piece of O1 or similar and make
a firing pin. If you need one..Ill dig though the stacks.

Yup. I came to that conclusion over the weekend myself. I don't owe
this metal anything, and if I don't know what it is, or how it behaves,
spending an afternoon on something complex only to have it be unusable
(the bolt, not the firing pin) would be silly, when known material is
readily available. Relative values and all that.

So what do I do with this accumulation of unknown steel then? And, more
importantly, why am I asking _you_? (written with a smile, I assure
you)

Btw...as I recall..the Thompson was never meant to have a light
trigger. You yank it, not squeeze it.

can't/won't train myself to do that to a trigger. It's reasonable as
reworked which is as good as I can expect to get. I learned enough
making the first pin out of "mystery metal" that I now know how to jig
it, which order of operations, and so on. So I'll get some of the right
stuff and make one just like it but better. (and save this one as a
spare, because it does work).

I'll post some pics if there's anything picworthy.

And polish the hell out of all the surfaces. Even those that touch the
frame/rub on the pin holding the trigger/sear you would be surprised
what polishing those can do, or at least in my 1911 they did/are "aint
quite done yet "

On 19 Mar 2006 10:43:44 -0800, redice wrote:
And polish the hell out of all the surfaces. Even those that touch the
frame/rub on the pin holding the trigger/sear you would be surprised
what polishing those can do, or at least in my 1911 they did/are "aint
quite done yet "

Deburring is the first thing I did. OK, I'm not a master machinist by
any means, but FFS, if I leave a burr, I clean it up. Kahr doesn't seem
to be all that careful about such things. There was a burr, for
instance, which was bearing on the side surface of the trigger, next to
the pivot pin. Absolutely worst possible place to leave a burr, guys.
Overall, I'm OK with the fit and finish. I realize that expecting a
match target quality trigger from _any_ production gun, as shipped, is
unrealistic. I'm having fun getting it as good as I can, but the design
isn't really made for that. If I make a new bolt I can give the firing
pin a much wider bearing surface with the sear, which gives me many more
options for tuning the sear engagement. As it, it's a 1/8" wide firing
pin bearing on a 1/2" wide sear. I can keep the same area of engagement
with a much shallower area of contact, which I think may help. Needs
some quality time on the mill, and I don't want to screw up the original
parts I have, so that's the motivation for making my own bolt - the
overall dimensions are of course right but the way the firing pin
channel, in specific, is executed is not the way I want to do it. i'm
envisioning something very much like a M1903's firing pin by the time
I'm done. (If I can use a M1903's firing pin parts, so much the
better).

On Sun, 19 Mar 2006 21:12:22 -0500, "Tony"
wrote:

The 1927a1 has compromises (as most full to semi conversions have) that were
made when the gun was re-designed from the full auto to the semi auto
configuration, for legal reasons.

The full auto was open bolt fixed firing pin with a wide engagement surface
on the bottom of the bolt, and the semi is a closed bolt with striker firing
pin, with narrow engagement surface. You can improve the pull by slightly
reducing sear engagement (not by filing the sear top but by building up the
bottom of the notch), and by limiting trigger overtravel. With a crisp
trigger you can fan it pretty effectively.

And put on a BMF Activater




I'm having fun getting it as good as I can, but the design
isn't really made for that. If I make a new bolt I can give the firing
pin a much wider bearing surface with the sear, which gives me many more
options for tuning the sear engagement. As it, it's a 1/8" wide firing
pin bearing on a 1/2" wide sear. I can keep the same area of engagement
with a much shallower area of contact, which I think may help.




"A prudent man foresees the difficulties ahead and prepares for them;
the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3

Dave,

I bought some of this steel from Brownells about 10 years ago and have fabricated
firning pins from it that have survived many 1000's of rounds in half a dozen
rifles:

http://www.brownells.com/aspx/ns/sto...%22+STEEL+RODS

It's pricey, but it works. I had to replace the all firing pins in my Rem 788's
because the originals were flat sided and kept eating up the firing pin springs
and jamming up the actions (wouldn't open). This is good stuff and a little goes
a long way. It machines very well.

FWIW, I tried drill rod and had breakage problems with it. Probably because of
my lack of skill at heat treating. This stuff requires no heat treatment.

Highly recommended.

Mike Eberlein

Dave Hinz wrote:

On Sat, 18 Mar 2006 10:57:29 GMT, Gunner wrote:
On 17 Mar 2006 18:16:42 GMT, Dave Hinz wrote:

(4140)

Any thoughts on where I should shoot for on the
hardening?

50-52//just as a gut feeling.
Is the sear carried on the bolt?

No, but of course that leads to the followup question. The firing pin
on the 1927a1 rides with the bolt, and is a piece of 1/8" flatstock cut to
an interesting contour. I made a new one (broke the firing pin tip off
of the original one due to my sear spring reduction experiments).
However, after only a few hundred rounds, the firing pin where it mates
with the sear, is showing rounding. It's unknown alloy. An point in
trying to harden that, at least in the part which meets the sear? I'm
completely ignorant of heat treating, which is pretty obvious at this
point, but I'm thinking get that local area of the firing pin up to
cherry red or so, and quench in oil?

Without knowing the alloy, I know it's a crapshoot. But knowing the
person I got these materials from, if it's newer than 1970 technology
I'd be shocked. Any thoughts?