How to get 3750 fps and a very lucky day

[Viperdoc]

I admit to being a relative beginner in CF reloading (at least for rifles), and have been posting about my attempts at improving the accuracy of my AR. Yesterday I loaded forty rounds in 223 with new Lapua brass, CCI BR primers, and Sierra 53 MK bullets, and 26.3gr H335 (0.4 below the book max). Have shot this combo before with no pressure signs.

Average velocities were around 3375 or so, and after over 30 rounds with pretty consistent results, I fired one round that was clearly different in sound and recoil. The chronograph said this round went out at over 3750 fps!

I dropped the mag, and saw smoke coming out of the receiver, and tried to work the bolt. No luck, the case was severely stuck in the chamber- broke two cleaning rods driving it out through the barrel, and then with a drift I tapped on the BCG, and the case came out.

Of course, the primer had blown, and there was a big imprint of the bolt face and extractor on the case head. There was a large, sharply defined expanded ridge just above the case head, but the case luckily did not separate. Glad I had glasses on, as always.

There is no way this case could have been double charged- the loads were enough to come to at least the base of the neck. Been using 0.003 neck tension- could the bullet have either jammed into the lands on feeding or been pushed back into the case?

Although I admit to being a novice reloader, I have a graduate degree in organic chemistry, and familiar with balances, scales, and the importance of being accurate and careful, as well as controlling all variables in experiments.

I think I was very lucky today, but am also concerned that I still cannot come up with why or how this happened. What should I look at to see if the rifle is damaged in any way prior to shooting again- everything seems to cycle just fine, and the firing pin and bolt face look fine.

Any help or ideas would be appreciated.

 

[TheSnake]

Lucky indeed. You mention that you broke two cleaning rods. What kinds of rods were they and how did they break? I would think the barrel could have been damaged by the cleaning rods at the least. In your current situation, I would take it to a smith for a good look over for sure.

With H335 powder, you would have needed around 30.4gr to get 3750fps in a 20" barrel and more for anything shorter. That is at 112.6% load ratio. Chamber pressure would be around 98500psi. Max pressure is 62366. I don't think you could stuff that much powder in the case. I would be looking somewhere else for the cause. Some type of obstruction in the barrel or a freak bullet? Maybe a good smith could help determine the cause.

I am interested to hear what others say here.

Robert.

 

[camac]

A simple possibility is shell length. Too long, jammed on bullet in throat and can lead to similar result. I had this happen once many years ago - no chrono but am v. careful with shell length now. Donuts can do the same by jamming the bullet too.

 

[JRinCo]

There's no problem getting 30 grains of H335 in a .223 case, how you might have done that I have no idea. 30 gr. of H335 behind a 53 gr. bullet would certainly produce the results that you got.

For P-dogs I use 29 gr. of H335 under a 30 gr. Berger with great results, but it's definitely a max load for a 30 gr. bullet.

 

[shootsanything]

Very lucky indeed - but it has happened to most of us at some time....

A few possibilities I can consider
1) Case being too long as mentioned above
2) Bullet being seated too deep when the AR bolt closed as you mentioned. What you may want to do is pull your firing pin and slam 1 or 2 home to see if they change length. You cannot baby an AR bolt, they have to be slammed and this means you need good neck tension to keep the bullet from moving. The bolt is designed to be slowed down in the act of pulling a round from the mag and is moving really fast when it closes.
3) Was it a hot barrel and did the case sit in the chamber for a while? Although I do not have experience with H335, I did find out the hard way that IMR4320 gets really HOT when it is really HOT.

 

[Recko555]

As far as damaging the barrel. If the cleaning rod went inside the case of the cartridge, I don't think you did any damage. Damage to the crown could of happened if you weren't careful.
Sorry no input on why this would happen, but the case being too long sounds reasonable to me.

 

[clowdis]

I have had the following condition happen on numerous occasions while reloading Varget into .308 cases. It involves the powder bridging in the funnel or powder measure. While it is less likely to happen with ball powder, it will all depend on the size of the throat of your measure or funnel. I've had powder bridge and overload the next case by 5 or 6 grains or up to 20 or more (overflowing). In my case I've been able to catch all of them that I know of, but varget is a much slower powder than 335. If this happened to you then it's easy to understand how you got excessive pressure. Always do a visual check of the cases before you seat a bullet.

 

[Viperdoc]

I always check visually the powder levels in the necks before seating. Also, all of the cases were new Lapua that had been FL resized, chamfered, and trimmed to length. I may consider doing even tighter neck tension, was doing 0.003, which should have been enough.

I did bend up an aluminum multipart rod, and then broke my fine Tipton carbon fiber rod. Finally just mounted the upper loosely and upside down in a big vise, and then tapped on the BCG with a punch and plastic mallet, and it came out easily. Visual inspection of bolt face, firing pin, and extractor all looked good.

The ridge just above the head of the case was very sharp- is it possible the gun fired without the bolt being completely closed (was not a slam) and the case not being completely chambered? Just a thought.

What should I be looking for to see if the gun is still safe? I know some advice has been to have a gunsmith look at it, but what will they be checking?

Will definitely be looking at powder levels more carefully- told my son that since he likes shooting perhaps he should try all of our new loads first- he respectfully declined.

 

[clowdis]

viperdoc,
The only way to get another 375fps out of a round is to add more powder or use a faster powder. You can't crimp it in or put it in with neck tension or head space or any other similar loading technique. Somehow you got too much powder in the case. Happens to most of us at some point. You can have a 'smith look over the bolt to make sure the lugs are OK if that makes you feel better. A slamfire won't give you higher muzzle velocity so I doubt that was what happened either. Besides, a slamfire will usually take out the magazine for you.

 

[AKDaddy]

My vote goes to a case that was too long, as others have mentioned.

I once neglected to check the length of some 257 Wby cases and began blowing primers abot one out of three shots. I dropped the powder charge of RL-25 by 3 grains from what was previously safe and still managed to get a 110 gr Accubond to leave the barrel and light up the chronography to the tune of 3850fps. Naturally, the primer was blown, the bolt had to be pounded open, the extractor slipped off the case rim, and the case had to be tapped out of the chamber using a cleaning rod. Sound familiar? I was stumped until I checked the length of my cases. Many were over length. After trimming the cases everything went back to normal. Lesson learned. Now I check my cases regularly and trim when needed.

 

[camac]

viperdoc,
The only way to get another 375fps out of a round is to add more powder or use a faster powder. You can't crimp it in or put it in with neck tension or head space or any other similar loading technique. Somehow you got too much powder in the case. Happens to most of us at some point. You can have a 'smith look over the bolt to make sure the lugs are OK if that makes you feel better. A slamfire won't give you higher muzzle velocity so I doubt that was what happened either. Besides, a slamfire will usually take out the magazine for you.

Clowdis, I am not sure of resulting velocity increase when I did this (as didn't have it on chrono), but jamming the neck down tight around bullet in breach is a lot different to crimping. The brass has nowhere to go so bullet is swaged through a narrow opening. If for instance you have a 223 deeply seated and push the neck (say 15 thou brass thickness) up into throat. The .224 diameter bullet has to be swaged almost full length through a 0.194" hole. I can tell you the pressure was extreme. I can't help but imagine holding a projectile back and building up 80-90,000psi could do anything but increase velocity substantially. i will never do it again.....
Although viperdoc has written this one off as he trimmed cases.

 

[white121]

Mabey you accidentally seated a 6mm bullet? That would cause some serious pressure! Just a thought. I have found the wrong size bullet in a new package before.

 

[Viperdoc]

I do have some 6.5 bullets on the same bench, but never the same time. They look huge compared to the .224's. Two other things I did notice- somehow with the Berger 62 bullets I tried, they often failed to chamber (even though made to the same magazine length), and when this happened the bullet was often jammed back into the case.

Although with the 53 Sierras I was shooting at the time this never happened (that I was aware), I wonder if the round going up the feed ramp might have pushed the bullet back into the case.

I think for the next group of reloads I am going to run the cases through a 0.245 neck bushing, which ends up with a little over 0.246 in the finished neck, and around 0.250 in the loaded round. Perhaps the increased neck tension would help.

Guess the final assumption is that I somehow got too much powder into the casing or the bullet got jammed back into the case, or came loose and jammed into the lands. Regardless, there was a lot of pressure involved. Not good.

 

[Ackman]

About going 3750......maybe not with 335 powder and a fast twist AR, but maybe not so impossible.

Several years back I picked up a new 26" Rem. fluted varmint takeoff barrel at the gunshow, .223. Never had a factory chamber like this, 0 freebore.....a 50BK touching the lands is right at the neck/shoulder junction. Doing a load sequence to see what this VV powder would do in this particular barrel....IMI brass (important), 7-1/2 primer, VV133 powder and 50BlitzKing.....I won't post the loads, but the last three groups were:
3645 - SD 11.8 - 3 shots .550"
3713 - SD 12.0 - 3 shots tight cloverleaf .215"
3753 - SD 8.0 - 4 shots .605", 1st 3 into .175"
Same loads, 50TNT's shot best at the lowest speed and opened way up going faster. I'd expected that.

Standard .223, shot during the summer. Those speeds were a surprise. No hard bolt lift, flattened/cratered primers, ejector marks, etc......no signs of overpressure. Shooting without a chrono or knowing the loads, other than accuracy a person would never know they weren't shooting factory ammunition.

In a 26.5" Shilen barrelled .223, 14 twist and a lot of rounds through it.....VV133 pushes 55gr Blitzkings at 3649, but not accurately. With VV135 and that same 55BK, accuracy at 3628 is one small ragged hole, SD is 10.2.

 

[fullersson]

I'm not sure what type of powder dispenser you use (if you even use one), but on mine you have to make sure all the powder is out of the tube before you change powders. I only mention this because it seems like you may also load for pistols. If this is a possibility only one or two rounds should have been affected, but it would really cause pressure problems. Good luck.

 

[camac]

OR - some powder from previous loading left in thrower when changing out.

 

[4xforfun]

Do you weigh each charge?

Funny thing happened to me a few years ago. I weigh EVERY charge. RCBS 505 Ballance beam. Something seemed "wrong" with my dispencer. It started throwing way light in the middle of a batch. I made some adjustments to my powder dispencer (I trickle the last few 1/10ths on every charge) and kept going. All of a sudden a very large fly flew from behind the scale......It had landed on the far end of the beam on the back where I couldn't see it!!!!!!

Made a HELL of a difference .

 

[Viperdoc]

I have been weighing with an electronic balance, or using a measure (Redding BR measure). In this case with H-335, it was with the measure. I throw and weigh a charge every ten throws, just to check. Even with the ball powders, I do not find it so consistent, even though I have been really trying to work the crank the same way every time.

It is an OK measure, but I have been lusting after a Harrel's meter. Anyone have any experience with one of these? Are they that much better in terms of reproducibility?

 

[btm_54]

Mabey you accidentally seated a 6mm bullet? That would cause some serious pressure! Just a thought. I have found the wrong size bullet in a new package before.

I have had that experience with bullets before as well.

 

[Ackman]

Mabey you accidentally seated a 6mm bullet? That would cause some serious pressure! Just a thought. I have found the wrong size bullet in a new package before.

Trying to seat a 6mm bullet into a .22 sized neck, you'd know immediately something wasn't right. And if someone managed to cram a 6mm bullet into a .22 neck, it wouldn't even come close to chambering.