safety and barrel life for hot loads

[IsleofGough]

I have many year experience shooting match grade rounds in match grade rifles in the military and civilian sector but am new to reloading. I discovered recently I can get an improvement from an average 0.6 MOA accuracy to 0.3 to 0.4 MOA accuracy from a bench at 200 yards with a mil spec M40A3 by handloading 155 gr sierra BTHP with 46 gr varget, CCI BR primers, 2.206 ogive length compared with factory match ammo. I've recently been experimenting with the 47.8 gr varget/155gr scenar combination recommended on several sites. The person who is teaching me handloading feels this is too hot and may not be safe and might prematurely wear out my barrel. It is very accurate and the primers look ok, but the case (Lapua brass) has its stretch on the body within a mm of the back of the case (unlike the 4 mm with the 46 gr varget/sierra bullets. Is this an issue I should worry about? The bolt is stiff but doesn't stick. FWIW, 47.8 gr varget fills lapua brass up to the bottom 1/3 of the neck and requires some compression to get the oal just short enough to not have to hand feed the rounds.

 

[Victor N TN]

Re: safety and barrel life for hot loads

Of course the final decision on what to load (as in powder charge if you have already decided on a given powder and bullet) is something that you have to make on your own. But hotter loads will DECREASE your barrel life for accuracy. A barrel that may normally get 2,000 rounds before accuracy starts to drop, with a very hot load may see a decrease in accuracy at 1200 to 1500 rounds.

I'm not saying that's going to happen to your rifle. But that's how it works.

 

[Greg Langelius *]

Re: safety and barrel life for hot loads

Stiff bolt lift is the Great God Pow's warning that you are twisting the tail of his pet dragon Whammo. Some care, some don't.

Metal fatigue is a concept that is based upon an engineering concept known as MTBF, or Mean (average) Time Between Failures. In this case, it refers to the number of pressure cycles a barrel will tolerate before its elastic limit is exceeded.

This is a totally separate issue from throat life. When a pressure vessel fails, it is often not because it is currently being stressed beyond its design limit. It is usually about how much and how many times it was overstressed previously.

Please note that Hodgdon's website lists 47.0gr of Varget as the max load with the Sierra 155gr HPBT.

Wisdom is an attribute usually based upon experience. Keep exceeding published limts, and you'll catch up on your experience real quick-like.

After what you've disclosed about your rifle, if you put it up for sale, I wouldn't buy it even on a dare. It's been abused.

Greg

 

[IsleofGough]

Re: safety and barrel life for hot loads

Thank you for your warnings. The 47.8 grain load is recommended:
http://optimalchargeweight.embarqspace.com/#/ocw-load-recipes/4533485759
and
http://snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1746511
and
http://www.snipercentral.com/forums/view...373a9f6a6f170c8
and several other sites.
But I'm assuming all these people destroyed their rifles. My abused rifle (back to shooting sierras at 46 gr until I get word on safety) shot three 5 shot groups under 1/4 moa at 200 yards today. As mentioned, though, I know very little about reloading, which is why I asked.

 

[former naval person]

Re: safety and barrel life for hot loads

Safety and economy sometimes come together. The rule of thumb I learned many years ago, was, when working up a load, measure the base of the case just ahead of the cannelure. When the loads increase the diameter of an unfired case by .001 STOP. You can increase it a bit more but when it gets to a powder weight that increases it a .001 more, that same charge will keep increasing the base til a primer falls out. May take one maybe three reloads. So...you are wearing out the case too fast, IMHO. I take it to the first .001 and then work back to the best accuracy node. MY belief. FNP

 

[IsleofGough]

Re: safety and barrel life for hot loads

Thank you. That is useful. I'll measure it.

 

[MitchAlsup]

Re: safety and barrel life for hot loads

The 47.8 gr Varget load is for WIN cases, the load should be in the 47.4-5 range for Lapua cases.

 

[IsleofGough]

Re: safety and barrel life for hot loads

Thanks. I saw the recommendation to drop the powder 1% for Lapua cases. Even so, that is a hot load. Testing today, it looks like the scenar is significantly less accurate at 300 yards and under (all I could test) compared with a sierra 155 grain MK (not Palma) with < 47 gr varget. If my barrel wears out prematurely, it isn't worth it to me the additional accuracy at long range with the scenar.

 

[Greg Langelius *]

Re: safety and barrel life for hot loads

...Which is why I responded...

Once you've <span style="font-style: italic">seen</span> someone blow up a gun, a lot of things suddenly click...

(Cherry Ridge, late '90's, pressure excursion(s?) due to excessive case neck length in handloaded ammunition. Range Officer's girlfriend's rifle using ammo he had built. Some were long some weren't, several of each were fired before the failure, impossible to determine pre-firing length of the cartridge involved. Only warning was hard bolt lift, which was ignored.)

I have no motivation to mislead you, but seeing those links just plain stops me dead in my tracks.

I guess I can't argue with logic like that. Enjoy.

Greg

 

[Unsichtbar]

Re: safety and barrel life for hot loads

You will note that the load data you referenced 47.8 Varget was fired in a 7.62 chamber AIAW and is loaded out to the lands. While it is true that generally 47.5 Varget is max in a Lapua case for a 155L and it is also true that in a Winchester case the load is considered to be around 47.8.

Another factor is that Varget has been known to vary lot to lot. I know the person that shoots this load and posted this OCW test, to receive feed back on the results for his use.The link you failed to read or list was the full test http://practicalrifler.6.forumer.com/viewtopic.php?t=862 He is in no hurry to damage him or the rifle.

When you start hitting speeds around 2900-2950 fps the barrel ware does increase. Usually the barrels are checked about 4500 rds if the accuracy is falling of they are bumped back. If we were shooting 175 gr at 2600 fps barrels have lasted 6000-10000 depending on accuracy requirements.

All these factors have to be having considered and loads should be developed for your rifle chamber combination worked up starting low slowly upward, looking for any pressure signs and a hard lift bolt is defiantly a sign, but you should have been working up from 46. Slowly.

Here is an example the Mfg. listed max for this powder is 45.3 these fellows did not start there. They knew they had an ultra tight chamber and bore so they started at 43 gr. good thing they did. I shoot this powder in my rifles and it is safe with absolutely no presure sigh the load is over 45.3 and runs a 155 Lapua out of a 22" Barrel at 2920 fps.

That’s a reason I do not post loads and prefer to show people how to develop a load, some people around here grab on the what ever is top load shove in a rifle and are surprised when their bolt is a hard lift. There is a load in the reloading section that list 49 gr of RL15 in a case, now that’s nuts, maybe it’s the worlds sloppiest chamber with a lawyer inspired length to the lands (unable to seat a bullet near it. I whish that load was not the because some one might come along and load it up.