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Semi Auto Crimping

lpaalplpaalp Member Posts: 947 ✭✭✭
Recently began tightening the crimp on .45 ACP reloads, meeting the specs in the sticky on the subject.

Ques 1: Does tightening the crimp affect POI, all other factors being the same?

Note: POI on the 1911 appears the same as earlier rounds; tight groups. The Glock, however, showed less accuracy and larger groups than with earlier (looser crimp) rounds.

2) I loaded 150 rounds at one sitting, exactly the same, fired 75 thru a Glock 21, and 75 thru a 1911. The cases of those fired through the Glock are 'smoked' very black around 1/3 of the case and about 2/3 of the length of the case. Those fired thru the 1911 are 'clean' (normal) - not excessively blackened. Memory says the Glock didn't blacken the cases or rounds fired with less crimp (although memory could be flawed; not certain, just didn't notice it with earlier rounds).

Ques 2: Could the tighter crimp cause more blackening in the Glock?

Note: I'm sure the 1911 has a tighter chamber, although I'm unable to measure. One reason I went to a tighter crimp was because of an occasional FTF in the 1911 with the earlier (looser) crimp. (Problem appears to be solved by the tighter crimp.)


  • perry shooterperry shooter Member Posts: 17,390
    edited November -1
    Normally smoked cases come from a poor seal of the brass case to the Chamber walls.upon firing I would keep the cases shot in the 1911 separate from those fired in a glock. different brands of brass can be thicker or thinner than other brands. the 1911 Has lands and grooves and the bullet will have higher pressure quicker to seal the brass than a Glock with how the rifling is made in a Glock I can't really explain why the group size went up in the glock but not the 1911.
  • noyljnoylj Member Posts: 172 ✭✭✭
    edited November -1
    All you want is to remove the case mouth flare. For revolvers and cartridges that head space on some datum other then the case mouth, a roll crimp can be used and more roll crimp can have a minor effect on pressure/velocity.
    Crimp can definitely affect accuracy, however.
    Why did you tighten the crimps? Was this because of failure-to-feed? If so, did you remove the barrel, blacken a round, drop in barrel, and verify that the case mouth was the hang-up?
    Round won't chamber?_"the solution is always the same:
    Take the barrel out of the gun. Drop rounds in until you find one that won't chamber. Take that round and "paint" the bullet and case black with Magic Marker or other marker. Drop round in barrel and rotate it back-and-forth. Remove and inspect the round:
    1) scratches on bullet--COL is too long
    2) scratches on case mouth--insufficient crimp
    3) scratches on case at base of bullet--bullet seated crooked due to insufficient case expansion (not case mouth flare) or improper seating stem fit
    4) scratches on case just above extractor--case bulge not removed during sizing. May need a bulge buster.
    If you want to measure the crimp, then the case mouth should be 0.4739-0.4736".
  • TriumphGuyTriumphGuy Member Posts: 37 ✭✭
    edited November -1
    Crimp autoloading rounds all you want, taper or roll. Look at some factory rounds. They roll crimp the daylights out of brass to secure the bullet, increase bullet pull on firing, and make the round more rugged for its bumpy ride into the chamber. The not-so-dirty little secret is that if the case is trimmed to specified length, the case mouth does not contact the leade. The extractor holds the round in position against firing pin impact. SAAMI standard dimensions for chamber length exceed the maximum case length, both including tolerance. A case that contacts the chamber leade is in either too long, in a too short chamber, or is not being held properly by the extractor. The clearance is small, but is always there if the chamber and case are within tolerances. Handloader magazine has done several write-ups of this recently. It does no harm to believe that the cases headspace on the mouth, but they don't.
  • machine gun moranmachine gun moran Member Posts: 5,198
    edited November -1
    An overly-long and/or heavily crimped case can result in the case mouth entering the ball seat at the front of the chamber, preventing the crimp from opening and raising H*ll with pressure (as well as accuracy). The 1911 was originally designed as a controlled-feed, but with some types of modifications that are done to guns and especially to mags, the cartridge is actually knocked into the chamber, with the extractor then (hopefully) snapping over the rim. If it doesn't, the extractor will jam the cartridge as far into the chamber (and into the ball seat) as possible. I'm a traditionalist, I prefer to blow my case heads with overloads, not with improperly assembled ammunition.[:D][:D]
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