I recently acquired an M1917 that has been rechambered to 45 Colt. It still works with 45 ACP with moon clips. It's been 100% so far with the ACPs and moon clips, but I've been getting failures-to-fire when firing 45 Colt. Sometimes it's just one or two per cylinder, but sometimes it can be several in a row. The only 45 Colt I've tried so far is Magtech cowboy action loads. The rounds that don't fire all have a very clear but small and shallow primer dent. Could something like adjusting the strain screw help, or will I need something more, like a longer firing pin for the hammer?
M1917 Light Primer Strikes
- Thread starter erikpolcrack
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I think you need to check your headspace. What's good for .45 ACP with moon clips may be too great for .45 Colt. BTW, the strain screw should be fully tightened, not adjusted.
Just a thought...
Any end shake?, a shim might push the cylinder back a tad.
Any end shake?, a shim might push the cylinder back a tad.
A knee-jerk reaction rather than any certain knowledge:
An adjustable spring kit (Miculek's being the only one I know about) cautions against going lower than a 7 lb. D.A. trigger pull, lest you experience FTF. If (IF) this gun strikes you as having a rather light D.A, trigger pull, then maybe-----------------------??
And as noted above, the strain screw is not there as an item to be adjusted. If it's backed off (or shortened), then things are NOT as they should be---------unless the mainspring is other than S&W-----unless (again) it is, and has been modified. Comparison with a known original (or the specs) is the only game in town for such a determination.
Ralph Tremaine
An adjustable spring kit (Miculek's being the only one I know about) cautions against going lower than a 7 lb. D.A. trigger pull, lest you experience FTF. If (IF) this gun strikes you as having a rather light D.A, trigger pull, then maybe-----------------------??
And as noted above, the strain screw is not there as an item to be adjusted. If it's backed off (or shortened), then things are NOT as they should be---------unless the mainspring is other than S&W-----unless (again) it is, and has been modified. Comparison with a known original (or the specs) is the only game in town for such a determination.
Ralph Tremaine
I think that this is the problem. If the cylinder chambers have been reamed to .45 Colt length with no other modifications, it's likely that the .45 Colt cartridges are headspacing on the case mouth instead of the rim. As most .45 Colt ammo has a roll crimp, the headspacing will be inconsistent.
Insert a .45 Colt cartridge and look and see if the rim contacts the cylinder face. It likely does not, and so will never be reliable with .45 Colt ammo.
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Seconding the above comments on the strain screw. I bought a used but not abused M15 recently. It had the smoothest DA I've felt lately. Misfires abounded. The strain screw had been shortened by about 1/8 inch. Took a new screw and a Wilson mainspring to get to smooth but heavy with 100% reliability.
If it chambers both 45 colt and 45 acp in full moon clips the problem is head space unless it has a ring around the outside edge of rear cylinder face. A 45 acp in a moon clip needs a bare minimum of .037 for clip and .049 for the rim a total of .086 from cylinder face to recoil shield (more like .090 on a factory cylinder) a 45 colt has a rim just .060. That is .026-.030 of head space and way to much and you firing pin is barely touching the primer. A firing pin should stick out of the firing pin bushing about .050 for a normal headspace round in order to crush the primer enough. Your headspace and a normal firing pin (ya I know it is called a hammer nose by the purists)
But even if you have a stronger mainspring and a longer hammer nose if you have excessive headspace you are beating your gun up. Firing pin hits primer and drives brass way forward then IF it does go off the brass gets a huge running start accelerating even faster than the bullet as it is lighter, before it slams into your recoil shield. In high powered rifles excess head space is a serious enemy which destroys brass and can shear of the bolt lugs
It is possible that whoever reamed the cylinder reamed it so that the 45 colt brass is SUPPOSED to head space on the front case lip, but as most 45 colts use a roll crimp that methoid is kind of IFFY.
There are only 2 positive ways to make a cylinder fire both acps and colts. One is this method where thew center of cylinder is recessed for 45 acp in full moon clips and the 45 colt rims set and head space on the outer ring.
The other method which I just used to set up a 325 is to use a 45 acp cylinder that I reamed the chambers to 45 colt length and a 45 colt extractor that has been had the ends of the arms thinned enough that 1/2 moon clips hold headspace for acps working off factor outside edge and eject them and the 45 colts head space off the center portion of the colt extractor
Notice how the colt rims set proud above the outside face of cylinder and the acps 1/'2 moons moon clips set flush
here is 3 acps in a 1/2 moon and 3 45 colts
But even if you have a stronger mainspring and a longer hammer nose if you have excessive headspace you are beating your gun up. Firing pin hits primer and drives brass way forward then IF it does go off the brass gets a huge running start accelerating even faster than the bullet as it is lighter, before it slams into your recoil shield. In high powered rifles excess head space is a serious enemy which destroys brass and can shear of the bolt lugs
It is possible that whoever reamed the cylinder reamed it so that the 45 colt brass is SUPPOSED to head space on the front case lip, but as most 45 colts use a roll crimp that methoid is kind of IFFY.
There are only 2 positive ways to make a cylinder fire both acps and colts. One is this method where thew center of cylinder is recessed for 45 acp in full moon clips and the 45 colt rims set and head space on the outer ring.
The other method which I just used to set up a 325 is to use a 45 acp cylinder that I reamed the chambers to 45 colt length and a 45 colt extractor that has been had the ends of the arms thinned enough that 1/2 moon clips hold headspace for acps working off factor outside edge and eject them and the 45 colts head space off the center portion of the colt extractor
Notice how the colt rims set proud above the outside face of cylinder and the acps 1/'2 moons moon clips set flush
here is 3 acps in a 1/2 moon and 3 45 colts
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Oldengineer
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I really appreciate the objective data from steelslayer. Thanks.
StrawHat
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SGT ROCK 11B
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My advice is to avoid revolvers that have been rechambered. They are never 100% reliable, JMHO
At this point it is, and always will be, a shooter.
What is your intended use?
If it in any way involves accuracy, you won't get it with either .45 ACP or 45 Colt.
.45 ACP revolvers need to headspace positively off of the case mouth. Moon clips are a wildcard variable. Even the use of 45 Auto Rim brass won't help, as the bullet jump from case mouth to the shoulder of the throat is excessive.
Headspacing a rimmed cartridge like the .45 Colt is equally problematic, but for different reasons. If (and only if!) the new chamber throats are cut to precisely the same depth you may be able to achieve reasonably good accuracy with handloads. But, you'll have to trim your brass to exact OAL ideally determined for your headspace, and, you'll probably have to crimp with a light taper crimp using a 45 ACP die as your final load step.
An alternative is to buy a replacement cylinder for either .45 ACP or .45 Colt and have it fitted.
What is your intended use?
If it in any way involves accuracy, you won't get it with either .45 ACP or 45 Colt.
.45 ACP revolvers need to headspace positively off of the case mouth. Moon clips are a wildcard variable. Even the use of 45 Auto Rim brass won't help, as the bullet jump from case mouth to the shoulder of the throat is excessive.
Headspacing a rimmed cartridge like the .45 Colt is equally problematic, but for different reasons. If (and only if!) the new chamber throats are cut to precisely the same depth you may be able to achieve reasonably good accuracy with handloads. But, you'll have to trim your brass to exact OAL ideally determined for your headspace, and, you'll probably have to crimp with a light taper crimp using a 45 ACP die as your final load step.
An alternative is to buy a replacement cylinder for either .45 ACP or .45 Colt and have it fitted.
I agree, the chambers were reamed too deep for 45 Colt. You can confirm this by measuring headspace with a feeler gauge. I’m sure you’ll find the space between the 45 Colt case head to breechface larger than with the 45 acp.
Your simplest and easiest solution is to countersink the mainspring tension screw hole deeper or add a shim between the tip of the screw and the spring to increase the mainspring force. However it will increase the trigger pull.
The next easiest is to install a longer firing pin if you can find a longer aftermarket pin.
The best fix is what steelslaver posted; find another 45 acp cylinder and ream it properly so the 45 Colt headspace is no greater than 45 acp. If you reload, ream the chamber shoulders square and taper crimp your 45 Colt cases.
Or only shoot 45 acp (or 45 auto rim if you don’t want to deal with clips).
Or get another 1917 that’s unmodified.
Your simplest and easiest solution is to countersink the mainspring tension screw hole deeper or add a shim between the tip of the screw and the spring to increase the mainspring force. However it will increase the trigger pull.
The next easiest is to install a longer firing pin if you can find a longer aftermarket pin.
The best fix is what steelslaver posted; find another 45 acp cylinder and ream it properly so the 45 Colt headspace is no greater than 45 acp. If you reload, ream the chamber shoulders square and taper crimp your 45 Colt cases.
Or only shoot 45 acp (or 45 auto rim if you don’t want to deal with clips).
Or get another 1917 that’s unmodified.
First try some other ammo.
The small primer dent doesn’t tell you anything except what you already know; that the primer did not ignite.
The large dent on a fired primer is caused by the case/primer being slammed against the firing pin and breechface when it ignites. Deactivate a primer mounted in a case with WD40 and shoot it in a gun that fires reliably every time, all you’ll get is a very small dent in the primer. So it doesn’t necessarily mean anything is wrong with the firing pin, and usually it isn’t.
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As someone who has turned multiple 44 mag cylinders into 45 colt cylinders , made multiple 45acp/colt cylinders, turned K frame 22 cylinders into 327 mag cylinders, reamed several 22lr cylinders into 22mags and reamed multiple J frame 32 long cylinders into 32 H&R cylinders I beg to differ. I have never had a reliability problem, nor an accuracy problem.I can not think of a single time one has failed to fire because of the cylinder. They all have either factory throats or in the case of my 44mag to 45 colt cylinders much closer tolerances than the factory produced. There is some drop in accuracy when firing 45acps in a properly set up acp/colt cylinder, but it is not as great as many believe. When spring comes I will do a test using my machine rest and show the results
The issue here is poor head space caused by a poor method.
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