Effect of crimp on velocity

[38SPL HV]

Looked through some old information regarding the effect of crimp on velocity. A heavy crimp instead of a normal crimp can result in a significant increase in velocity; not to mention pressure increase. I had a heavy crimped +P 158 gr SWC loading chronograph an avg of 975 fps while the normal crimped loadings with the same bullet/powder/case/primer combination yielded 925 fps.

Have you every noticed Buffalo Bore's (BB) crimp on their 38 Special +P 158 gr SWC and LSWCHP loadings? They are pretty darn heavy compared to Rem/Win/Fed 38 Spl +P 158 gr LHP FBI loadings. Bet it helps BB achieve their velocity levels?

Any comments?

Your experiences regarding degree of crimp and velocities?

[DWalt]

I have never tested it, but my feeling is that the degree of crimping makes little difference in MV or chamber pressure. To test that hypothesis, one would need to make up precisely the same load with exactly the same cases (especially case length) and bullets, crimped and uncrimped, and the MV chronographed from the same revolver chamber firing at least 10 rounds (more would be better) each to calculate the average MV and SD of each. Then apply the T-test to determine if there is any statistically significant difference between the average MVs of crimped and uncrimped loads.

Someone may have already performed such testing, but if so, I have not seen it. The Lyman cast bullet handbook is very detailed in its discussion of all reloading information, but there is no mention made about MV differences between crimped and uncrimped cases. About all it says is that uncrimped cases provide more uniform bullet pull than crimped cases and accuracy is better. Their recommendation is that cases not be crimped unless absolutely necessary to keep the bullet in place (e.g., for use in a tubular rifle magazine or heavy-recoiling rifle or handgun loads).

[mtgianni]

I believe some ball powders burn better with a heavy crimp, I don't feel the same about flake powders.

[johngalt]

I think a lot of uneccessary ovecrimping goes on. With revolver cartridges, I roll crimp as light as possible so that bullets don't jump under recoil. I use factory ammo as a guide. I taper crimp auto cartridges just enough so they feed and use a plunk test as a guide.

I don't reload for rifle, but they use far slower powder in much larger quantities than pistols, and in general are only taper crimped for reliable feeding. This makes me think that a heavy crimp for pistol is not needed.

I have never tested for velocity changes (no chronograph), but I suspect any difference would be lost in the noise due to variability.

[fredj338]

Depends on the powder used. Slower powders benefit from heavier crimp. Fast powders show almost no vel diff.

[38SPL HV]

Thank you, particularly DWalt, who is very helpful and as always detailed/fact based in his responses.

Thanks again

[eb07]

Good info. I tend to go harder on crimp for my snub rounds and I have noticed a small FPS increase.

Accurate reloading covers it

THE EFFECTS OF CRIMPING ON ACCURACY AND VELOCITY

[forestswin]

Originally Posted by DWalt

.......

Someone may have already performed such testing, but if so, I have not seen it. The Lyman cast bullet handbook is very detailed in its discussion of all reloading information, but there is no mention made about MV differences between crimped and uncrimped cases. About all it says is that uncrimped cases provide more uniform bullet pull than crimped cases and accuracy is better. Their recommendation is that cases not be crimped unless absolutely necessary to keep the bullet in place (e.g., for use in a tubular rifle magazine or heavy-recoiling rifle or handgun loads).

Dewalt
The OP, 38SPL HV is discussing......WELL..38 special (what else)

The "not crimping" recommendation you are referring to is for rifles. Go to the chapter (14) page 60....top right. Mike V. authors it too.
He says a crimp is a must for handgun cartridges and goes on to recommend the fingernail method for the amount of crimp.

Yes, you mention handguns as an exception.....but it's a little confusing because the thread seems to me to be strictly about 38 special.

[Nevada Ed]

I have noticed that light crimping to heavy will effect my 38 special loads in my J frame snub.

The soft HBwc 148gr with a light crimp is very accurate with Bullseye in my M49.
However I can change the ES of loads by adding more crimp and
with some powder make the ES even higher.
Trail Boss can go from a 12 ES to a 23 with just a slightly heavier crimp.
Red Dot from from a 41 ES to a 73ES but also gain 21 fps.

With a 158gr soft lead and a slow powder a medium crimp with
one load does 812fps and with .1 more grain of powder and a heavy crimp,
this load will do 948 fps out of the 2" barrel.

This same powder .2 grs lower than the 812 fps medium crimp load
but with a heavy crimp will do 851 fps.

I am a firm believer that a heavy crimp on a soft lead 38 bullet............
does change the out come of what a load will do........

however I do not use a heavy crimp on any of my rifle loads with jacked copper bullets.
Maybe a med. light on a bullet that has a cannelure, above a medium loading.

[gman51]

I didn't crimp my 38 spl because the bullet maker said not to. Well two squibs and several bullets laying on the ground taught me crimp the dang casing. No problem after I crimped them.

[38SPL HV]

Nevada Ed, good info. I can't wait to get my chronograph.

Forestwin - "what else" besides the 38 Special - I have reloaded the following since I began in this great sport 45 yrs ago:

25 acp
32 S&W
32 S&W Long
380
9mm
38-44
357 Magnum
41 Magnum
44 Magnum
45 Acp
243 Win
7x57
270 Win
30-06
8x57

Be glad to share my experiences on these if you want.

[Rule3]

Originally Posted by 38SPL HV

Nevada Ed, good info. I can't wait to get my chronograph.

Forestwin - "what else" besides the 38 Special - I have reloaded the following since I began in this great sport 45 yrs ago:

25 acp
32 S&W
32 S&W Long
380
9mm
38-44
357 Magnum
41 Magnum
44 Magnum
45 Acp
243 Win
7x57
270 Win
30-06
8x57

Be glad to share my experiences on these if you want.

Gads how did you ever get a good crimp on those handgun loads?

[hdwhit]

The only round I routinely crimp is 38 Special. And I have noticed that with the slower burning powders it seems to have a slight improvement in velocity (maybe 25 fps), but a huge improvement in consistency (2-3% variation versus 7-10%).

[Collo Rosso]

Might be poor observation skills but I'd swear when using 2400 in 357 and 44 at magnum levels my loads with MCB coated SWC's and a good roll crimp burn cleaner than the Xtreme RNFP's plated and a light roll crimp. I know, two completely different bullets, but still..
One of these days I will buy a chrono.

[38SPL HV]

Rule3 - I'll be glad to share my reloading experiences with you - pls feel free to send me a PM.

[H Richard]

When working up loads, especially magnum or heavy non-magnum loads, a heavier crimp "normally" yields greater pressure, Velocity, and Accuracy. In this regard this is where precise trimming of the cases will show up, if the length of the case being crimped is much more consistent, the load will be more accurate. When minimal crimps are used, there will be minimal difference.

[firearmsunlimited]

Crimp can effect burn rate and accuracy.

[patrickd]

A decent crimp will help with combustion and therefor velocity in lower pressure cartridges like the 38SPL. This is especially true in the 38SPL when using Unique powder. Crimping helps to keep pressures up with slower burn rate powders and increases combustion efficiency at the start. It will also keep things cleaner in cartridges like the 38spl when loaded with Unique.

[gwpercle]

It depends on the burning rate of the powder.
Fast powders like Bullseye in target loads can get by with less crimp to get a complete burn. A heavy crimp will not help velocity in these loads.
Slow powders like 2400 in large charges used in magnum loads benefit from a heavy crimp, the heavy crimp allows more efficient combustion which results in added fps.
Gary

[WR Moore]

Crimp can help make pressures and velocities more uniform. Several years ago, the bench rest crowd discovered this applies even when you make sure your brass thickness is uniform (where the bullet rests) and all the same age etc. Rather than depending upon the brass tension to control powder burn.

For those who worry about "deforming" bullets by crimping them if they don't have a crimp groove: bench rest bullets don't have them and if the all-the-bullets-in-one-hole group doesn't find a problem, the rest of us won't notice a difference either.

[Brassmaster]

I noticed that questions have been raised whether crimp affects velocity and pressure. Although I cannot speak to crimp affecting velocity, readings of test material reveal that crimp can have a significant effect on chamber pressures. My understanding of one of the basic principles is, tighter crimps hold seated bullets longer, thereby allowing chamber pressures to build. Another equally important fact is that crimp has a direct effect on accuracy. Some research has been published on this subject. After 40 years of reloading .45acp for Bullseye competition and much Ransom Rest controlled testing, I have seen first hand the effects of crimp on accuracy at 50 yards out of an accurized 1911. To the point that I have arrived at an optimum crimp for my competition 1911s which I religiously Q/C the amount of crimp with calipers during reloading of rounds to be used during competition. Although I own and shoot .38 Special Revolvers and control the crimp on them, I do not have as much experience regarding crimp with them and do not believe that a roll crimp for a revolver is as critical as taper crimping. Just my opinions.

[sw282]

Crimping soft lead boolits will actually SWAGE them down a size.

Not good.. Crimp as little as possible to keep from deforming the boolit

[fredj338]

Originally Posted by Collo Rosso

Might be poor observation skills but I'd swear when using 2400 in 357 and 44 at magnum levels my loads with MCB coated SWC's and a good roll crimp burn cleaner than the Xtreme RNFP's plated and a light roll crimp. I know, two completely different bullets, but still..
One of these days I will buy a chrono.

Good crimp with slower powders allows for better combustion, cleaner burning, higher vel.