factory crimp lowers velocity????

[saands]

OK ... I realize it isn't Sunday morning, but I know that EVERYONE loves a good puzzle. I loaded up 50 rounds of 9x18 about a week ago. They are warm loads, but things look good with them out of my EG Mak. I have made it a habit to do the seat and crimp in two different steps, and I almost always use a Lee Fatory Crimp Die. I didn't have one yet for the 9x18, so I was seating in one step and then crimping with the seater/crimper die in a subsequent operation. They feed and work well. Last night my Lee FCD arrives so I stuck it in the press and started going to town, when it occurred to me that these loads were spicy and that I should be careful. So, I just crimped 15 of the 50 and figured that I would run both styles across the Chrony at the range ... which I did today. I was afraid that maybe the tighter crimp would cause a slight delay in the bullet leaving the case, and would therefore cause the pressure to spike and the velocity to increase. I fired 8 of each across the chrony and the SD was small in both groups (11 and 18 fps) and the average velocity for the FCD rounds was 1220 fps while the average for the non-FCD was 1260 fps

Does anyone have even a remote clue as to why this happened ... and no, I DID NOT confuse the batches ... the primers were CLEARLY marked distinguishing the two populations. And no, nothing happened to the Chrony between the batches, because I shot 3 of crimped and then 3 uncrimped and then 3 more crimped etc ...

I'm REALLY looking forward to your thoughts!!!

Bring it on

Saands

[MrApathy]

what powder were you using. burn rate can make a difference. would easily believe with some powders it increases speed other decrease.

[b_ionian]

This is an honest question; I'm not trying to be a jerk: Why would a 40 fps difference be of concern?

[saands]

VihtaVuori N350 was the powder ... can you elaborate?

I've been trying to think of any reason that more resistance would lead to lower velocities and what I am now suspecting is that, for whatever reason, maybe the FCD treatment somehow reduces the resistance ... but I can't really come up with a good reason why.

Saands

[saands]

That's a fair question ... the 40fps is of absolutely no concern. But, in general, things that behave in ways that are contrary to my understanding are always of concern ... not necessarily bad, but worth thinking about as they usually alert me to flaws or holes in my understanding.

Saands

[Bullet94]

saands

I’m not familiar with the 9x18 cartridge, but I believe your talking about taper crimping. The idea with taper crimp is to remove all the bell on the case mouth and help the amount of tension on the bullet so the bullet won’t be shoved into the case upon chambering. Maybe the uncrimped rounds are being pushed into the case when chambering causing more pressure when fired. Not sure if this is the answer but you could try chambering both the crimped and uncrimped rounds and then eject them without firing them and measure OAL and see if there is any difference. If there is a difference in OAL this could explain the difference in your fps.

[saands]

Well ... the 9x18 is completely straight walled, so this is actually a possibility. It seems odd that the results would all be SOOO uniform, but I will certainly check it out. It makes more sense than anything that I've been able to come up with

Saands

[Peter M. Eick]

As a pragmatist and a scientist, I say "so what?" If you are confident you did your experiment correctly and you got the results you were not expecting, then repeat the experiment. If it also gives you the same results, then maybe the premise is wrong. Try a different combination of events and run the test again.

The ONE thing I have learned with my Chrono is what you read, and what you get in your guns is not the same things. TEST EVERYTHING (to paraphrase Weshoot2's advice to me) and RETEST AS NEEDED.

Whatever you do, don't let your scientific biases cloud your interpretation of the results. Healthy skeptism of your techniques and equipment is fine, just don't ignore tested repeateable facts because they don't meet your biases....

[griz]

If the new crimp die squeezes the case fairly far down the bullet, is it possible that it is belling the case a bit on the rest of the bullet, reducing the resistance?

I've never loaded the 9X18 so count this as a guess.

Anyway, as pointed out already, do not ignore the possibility that what we think we "know" is wrong. I ran into that while testing the effect of powder position on velocity. I had assumed that the velocity would always be less when the powder was at the front of the case compared to back by the primer. But for one combination it was the opposite. I even repeated the test to make sure I hadn't did something wrong. So it's possible that more pull might not always increase pressure.

[zeke]

saands-did you special order the LFC ? Was considering doing this for the Mak (haven't reloaded for it yet), due to short bullet interference with the case.


Recently tried some of the newer factory Rem 44 mag 180 gn jsp's. Got very consistent 1900 fps from 7 1/2 in Bisley ((2100 fps from 16 in Marlin). Tried giving them a LFC, and velocities dropped slightly and became more eratic from the Bisley. Have put heavy LFC on Rem factory 38 special and 357 mag Golden Sabers, with significant improvement resulting.

There's always gonna be exceptions, no matter what our preconceptions are.

[WESHOOT2]

Confirm OAL; same?

Since (apparently) the only thing changed was the LEE die, test again re-using old die; same velocity range as prior lots?
Install FCD, test; same velocity range as first lot?

Perhaps the crimp is different. Slower? Because it is not sizing the case as much. Maybe.
If all other testing confirms lower velocity with FCD I'd say less sizing.)

[saands]

FCD for 9x18 ... yes, special ordered ... it did NOT take them 6-8 weeks like they told me ... more like 10 days including UPS ground shipping.

I still have some of each type:
OAL for the FCD: mean = 0.9702"
OAL for non-FCD: mean = 0.9699"

Looking at the standard errors of the means (statistically speaking) these two distributions are indistinguishable ... confirmed: "OAL same"

For clarification, these rounds were all made at the same sitting. I just sat down and reloaded 50 rounds for testing. They were all sized with the same full length sizing die. And they were ALL crimped with the Lee seating die. The FCD'd rounds were crimped twice ... once with the normal Lee seating die (I can never remember which is roll and which is taper ) and then a couple of days later with the FCD when it arrived. One thing that I was thinking is that the carbide ring on the FCD was putting the squeeze on the whole bullet and that the brass, being more elastic than the lead, may have sprung back after the "resizing" (thereby leaving the lead with less tension in the FCD'd rounds) ... but these rounds didn't get the FCD's resizing treatment ... I just tested it and I can insert the non-FCD rounds into the FCD with no more than moderate thumb pressure and even that is only needed to get the mediocre crimp past the carbide ring ... other than that they are a slip fit.

I will make another batch and try some with JUST the FCD as well.

Thanks for the ideas ...

Saands

[WESHOOT2]

Great reply.

Time may give rise to other possibilities.

[saands]

Following up on the "Maybe the FCD crimp is being more effective at preventing setback upon chambering" idea ...

I measured OAL before and after chambering several rounds (slide released from full back position ... firing pin removed from slide to make it less exciting ... just in case ) Only one round out of 5 exhibited any measurable setback at all and even that was only 0.002" ... and this phenomonon was present in 100% of the rounds fired at the range. I was actually rooting for it, but I don't think that this is the reason. This is pretty lively ammo, though, so I think that I will repeat this at the range with "real" loading forces ...

Wishin' I lived in the country ...

Saands

[caz223]

My guess would be that if you adjusted the FCD a bit tight, and that it sized the bullet smaller, just small enough to make it have less effort to size itself to the bore and rifling when fired. We know it post sizes the case, but the bullet is in the case, right? So it sizes the bullet, too.

[WESHOOT2]

I hypothesize that the second crimp is loosening the case slightly.

[saands]

Good one ... not only a WAG ... but a seemingly untestable one at that

I made another batch ... same recipe to the best of my ability. This time I also made some that have only the FCD (more like my real process would be anyway).

Stay tuned ... Data to follow.

Saands

[WESHOOT2]

I been wrong and right before.........

[rambo1937]

Where does N-350 appear in the burn rate table?

What charge are you using?

I have a 30.06 that shoots 100 fps faster with nickel cases over plain brass with the same load. Go figure