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45acp base to shoulder mesurement

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james r chapman
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243winxb
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Post by Lamar H Sun Apr 12, 2020 5:15 pm

Never took an accurate measurement on two pistols until today.
Both with Kart barrels installed by same gunsmith 
 With both barrels out seating 200 swc until flush with hood
one measured .950 base to shoulder the other .940 
Been using ,925 to .930 went down to .920 to get lighter
loads to function with ..465 crimp. Not as accurate in my
hands.
 What do you suggest as a compromise for both guns?
I no longer shoot full matches only short line.l

Thanks for your thoughts
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Post by 243winxb Tue Apr 14, 2020 5:21 pm

Head to shoulder .947"  for my Colt Gold Cup, 1970s gun ,  factory barrel, puts the bullet shoulder  touching the rifling. 

Lyman cast 200 gr bevel base sized .452"
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Post by Aprilian Tue Apr 14, 2020 6:49 pm

I follow what Jon Eulette has always suggested, .920'  one of many places he has posted the suggestion
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Post by 243winxb Tue Apr 14, 2020 7:49 pm

The .920" is the maximum chamber length listed by SAAMI.   The case  mouth would headspace on it. 
The bullet shoulder should be longer? 

Its  easy to seat a bullet long  and watch to see if the action fully closes.  While watching for rifling marks on the bullets shoulder. 

Maximum brass length & minimum chamber are the same .898" 

To answer the original question, i would load all ammo  around .935"  Base on the .940"  gun.   Also  looks like maybe ,  to much crimp is being applied? I taper crimp just enough so the round drops in &  out of the chamber.
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Post by dronning Tue Apr 14, 2020 9:26 pm

Aprilian wrote:I follow what Jon Eulette has always suggested, .920'  one of many places he has posted the suggestion
+1
I shoulder seat all SWC ammo (160g-200g) the same .920 for 4 wad guns.  I use to crimp everything at .469, now with light loads it's .463-.465 for lead, depending on brass.
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Post by Wobbley Tue Apr 14, 2020 9:41 pm

.930 is my measurement.  Crimp to .467-.468
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Post by james r chapman Wed Apr 15, 2020 3:24 am

.920 ish
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Post by 1joel1 Wed Apr 15, 2020 9:50 am

dronning wrote:
Aprilian wrote:I follow what Jon Eulette has always suggested, .920'  one of many places he has posted the suggestion
+1
I shoulder seat all SWC ammo (160g-200g) the same .920 for 4 wad guns.  I use to crimp everything at .469, now with light loads it's .463-.465 for lead, depending on brass.
+1, also per Jon.

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Post by David R Wed Apr 15, 2020 11:48 am

Plunk test.  
Most of you are working with a match grade barrel.

For the rest, remove the barrel, drop a loaded round in the  clean chamber.  It should fall in.   The brass should be flush with the back of the hood.  Some guns this is longer than others.  Adjust OAL so the  brass and hood are flush.  Shoot some groups.  This is headspacing the cartridge on the bullet instead of the case.  This can improve accuracy.    The only way to know is to try.  

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Post by Aprilian Wed Apr 15, 2020 12:11 pm

As lead is softer than brass, it seems like headspacing off the bullet could cause some guns to have light firing pin strikes since the firing pin energy would be split between engraving the bullet into the rifling and compressing the primer.

and from Jon...
Jon Eulette wrote:I would be cautious about seating too far out. I regularly see lead rings causing failure to fully feed when seated out too far. I seat with shoulder of bullet protruding from case mouth approx. 0.030". Some chambers are more forgiving than others on oal. I also hand cycle with out recoil spring to check feeding smoothness. Should be smooth transition from mag to chamber. Too long can cause glitch in feeding. Will still feed, but not smoothly. For best consistant cycling smooth is best. Hiccups in feeding cause vertical stringing.
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Post by James Hensler Wed Apr 15, 2020 2:22 pm

I was always told and have always done this. 
When I get a new barrel or pistol I make a finished rounds longer and slowly shorten it until I can barley spin the round in the barrels chamber. I was told to do this back in my Marine Corps Shooting days. I was told no two barrels are exactly alike. 
Is this wrong?


Last edited by James Hensler on Wed Apr 15, 2020 2:55 pm; edited 1 time in total
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Post by Jon Eulette Wed Apr 15, 2020 2:39 pm

Most recently built 1911's run 0.900 to 0.905 depending on who built the pistol. On rebarrel projects you can see 0.910-0.920 depending on the slide used on older pistols; dimensions typically run longer than newer slides being manufactured. Kart barrels in older slides run deeper and I use KKM barrels to control this. KKM true short chamber. Kart not short chambered enough and can sometimes run 0.910 before finish reaming the chamber. 
45 doesn't need to be seated close to the rifling. I don't know why they make a lead ring in the chamber when seated long but they do! I've seen chambers from 0.900-0.920 shoot 1" at 50 yds. 45 is very forgiving cartridge. So if it works in your pistol and your not having issues then run what you like. But I'm also a believer in not reinventing the wheel. And I like to say, I'd rather be a Master Shooter than a Master Reloader!
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