Primer Dimple Challenge Accepted

[tappedandtagged]

From Eric's thread entitled "How many times can you re-chamber a duty round?"


...........I would like to see this same test done over a period of time. For example, chamber a single round 5 times a day for a week, then 2 weeks. Maybe the primer will chip away inside, but over time it may actually start to dissolve due to exposure. Don't know how it would turn out, but should be a fairly easy test to complete.


I'll donate some ammo to this. I have on hand to test this with the following rounds;

Remington UMC 55 FMJ
Lake City M855
Personal reloads with Tula Primers (I may have fired the last of these off in my last range session)
Personal reloads with CCI Primers

I'll take three rounds from each, and do the following:

Rounds in group 1- chamber rounds 20 times consecutively, then fire them (one day)
Rounds in group 2- chamber them five times a day for a week, then fire them at the end of that week
Rounds in group 3- chamber them five times a day for two weeks, then fire them at the end of two weeks.

Do I need to extend this with a group 4? I personally don't see the time factor playing a role, but rather the actual number of times chambered. I have 20 year old primers I use in my 44mag that have been kept in the cardboard box with the primer cups open and exposed for that length of time. After firing 150 of them, they all go boom. But, if that's what you guys want to see, I'm willing to do it and test.

[tappedandtagged]

Ok, I haven't forgotten. Life has been a bit hectic getting ready for a new baby. I plan on getting to the range tomorrow to test the first rounds out.

It seems I have found some Colt branded ammo to test as well.

[tappedandtagged]

This is after 20 chamberings. I haven't noticed the simple getting any deeper since the first few chamberings.

http://i820.photobucket.com/albums/zz121/zlwhite/IMG_20140208_155852536_HDR_zpswiclfbpk.jpg (http://s820.photobucket.com/user/zlwhite/media/IMG_20140208_155852536_HDR_zpswiclfbpk.jpg.html)

http://i820.photobucket.com/albums/zz121/zlwhite/IMG_20140208_155833341_zpssv6xenfh.jpg (http://s820.photobucket.com/user/zlwhite/media/IMG_20140208_155833341_zpssv6xenfh.jpg.html)
The rifle is a Windham Weaponry AR with factory BCG, spring and buffer. Each chambering I made sure to pull the charging handle back as far as it would go and let it go without riding it at all.

Tomorrow I plan to fire the 20 chambering group as well as 5X a day for a week group. If it wasn't for the sharpie, I wouldn't be able to tell the groups apart.

On a side note, am I doing this for my own amusement and posting here for no reason? I can't tell if any of you guys are interested in this or not. Pipe up on your thoughts!

[UWone77]

I'm definitely monitoring this thread.

Like Eric posted originally, I'm one of those guys who gets extra boxes of ammo issued just to replace the chambered rounds.

I think you probably need a bigger sample size, but how many, I'm not sure.

[tappedandtagged]

I'll tell you, its a pain chambering all those rounds. I'm sick of it. I'm not entirely sure I want to do this with a larger sample size!

[Tzed250]

I am interested in the results. Not that you don't have your hands full, but data on a change in COAL would be interesting also.

[tappedandtagged]

Tzed250, I can do COAL measurements in the morning on the remaining rounds.

I fired off the first two batches. One with 20 charges and the other with a total of 35. They all went bang with no delay or hand fires at all.

I have four more remaining. The plans for those are to cycle them 5 times a day for the next week for a total of 70. Given the results today, I'm thinking I might need to extend this to more. The dimples are not appearing to be getting any deeper from the first few chamberings. This was very evident when I chambered the first batch 20,times consecutively. They looked like batch 2 on the first day with the exception of the case and bullet being battered.

So, stick to the plan or keep chambering them beyond 70. I'll be honest, the repeated chambering is tiring. I'm all for ending this in a week at 70 chamberings. Well, 71 with the 71st being when it will be fired.

[tappedandtagged]

I am interested in the results. Not that you don't have your hands full, but data on a change in COAL would be interesting also.

COAL at start:

Colt 62 grain- 2.228" No cannelure
M855 62 grain - 2.249" Crimped in cannelure. Headstamp is WCC 11
Federal -American Eagle 55 grain- 2.19" Crimped in cannelure (mistakenly called Remington 55 grain above, my apologies)
Handload with 55 grain Hornady SP- 2.195" Has Cannelure but NOT crimped
Note- 55 grain SP measured 2.144" at base of soft point/top of jacket. The SP has been mangled and worn by repeated chamberings)

COAL at 35 chamberings:

Colt 62 grain- 2.255" Yup, thats right, its pulling out at 0.006" longer. I measured several new in box ones to confirm the COAL at start was correct
M855- 2.243" Only 0.006" shorter
Federal 55 grain- 2.185" Or 0.005" shorter
Handload 55 grain SP- 2.203" and at the beginning of the jacket it measures 2.151"

I find it very interesting that the two non-crimped rounds are pulling out and the crimped ones are being pushed in. It seems the crimp is keeping the round from pulling out from the sudden stop in the chamber, but not keeping it from moving in when it hits the feed ramps. I did notice some copper shavings on the Colt round at the mouth of the case suggesting that the bullet is moving in and out quite a bit with the chamberings. I'll re-measure before I shoot these off at 70 chamberings.

[tappedandtagged]

70 chamberings has been accomplished! I do wish this had of been done with a larger sample; however I am not willing to repeat it as I'm done in. Even this last week with only 4 rounds remaining, its been a constant battle to remember to chamber them every day. I did notice that upon reaching day 12 the bullet on the non-crimped steel cased Colt 62 grain round was pulling noticeably out. A measurement of the COAL at the end of this project is below:

Day One Day 7 (35 chamberings) Day 14 (70 chamberings) Total difference
Colt 62 grain- 2.228" 2.255" 2.285" +0.057"
M855- 2.249" 2.243" 2.250" +0.001"
Federal 55 grain- 2.219" 2.185" 2.185" -0.005"
55 grain SP handload- 2.195 2.203" 2.197" +0.002"


These are only my observations. They were not done in a lab or in any type of controlled circumstances. They were done on my back porch sitting in a patio chair with only a Coleman Ice Chest to aid in capture of the rounds as they ejected.

In all, I fully expect all 4 of the remaining rounds to fire tomorrow when I go the the "range" (aka, my parent's house in the country). Will report back when I can. I'll take pictures before I fire them off as well and post back.

[tappedandtagged]

Quick post. They all went bang after being chambered 70 times. Pics of the dimple to follow.

[tappedandtagged]

Last post. This is the dimple I was left with after aggressively chambering the rounds 70 times.
http://i820.photobucket.com/albums/zz121/zlwhite/Mobile%20Uploads/IMG_20140216_175144350_HDR_zpsvdvnd0c9.jpg (http://s820.photobucket.com/user/zlwhite/media/Mobile%20Uploads/IMG_20140216_175144350_HDR_zpsvdvnd0c9.jpg.html)
http://i820.photobucket.com/albums/zz121/zlwhite/Mobile%20Uploads/IMG_20140217_104529320_zpsy55i0upr.jpg (http://s820.photobucket.com/user/zlwhite/media/Mobile%20Uploads/IMG_20140217_104529320_zpsy55i0upr.jpg.html)
http://i820.photobucket.com/albums/zz121/zlwhite/Mobile%20Uploads/IMG_20140217_104532692_zps9j4hwov5.jpg (http://s820.photobucket.com/user/zlwhite/media/Mobile%20Uploads/IMG_20140217_104532692_zps9j4hwov5.jpg.html)

[UWone77]

Great job, I'm impressed you chambered those rounds 70 times.

Realistically, I'm working 208 days a year, that's if I take no vacation and holidays. If I show up to work 170 days a year, and maybe if I'm lucky, deploy my rifle and chamber a round 5-10% of those times, that's almost 4 years of chambering. We also replace our duty ammo once a year. This has never been a big worry for me, but thanks for doing this and confirming what I pretty much already knew.

I guess the idea behind replacing the chambered ammo in our dept is the you never know factor.

[tappedandtagged]

I've only had my rifle for 2 years. In that time I've had purpose to chamber a round twice. One time I rode the bolt forward and utilized the forward assist. The other time was in a hurried manner and was chambered normally. That dimpled round was rotated to the bottom of my spare mag, just in case. I wish we shot out duty ammo once a year. Non-SWAT members are lucky to qual with their rifles once a year! Our training budget has gone to crap lately. If you want training, you have to join SWAT which trains once a month focusing on range time and building clearing/entry with the occasional bus assault thrown in.

[Tzed250]

I want to thank you for the effort on showing the effect of multiple chamberings on a round. Goes to show that a crimp into a cannelure is a safe bet.

[KevinBLC]

Besides the AR, are any other firearms made with free floating firing pins?

[mustangfreek]

Besides the AR, are any other firearms made with free floating firing pins?

SKS