Dear all

I was developing loads for my 7mm Rem Mag yesterday and worked up to an old tried and tested load in one of my previous 7mm's.

The load was 67 grns of RL22 behind a 160 grn accubond. I then decided to chrono graph the load and to my amazement and immediate concern these were the results.

Velocity readings as follow:-

3239
3246
3278
3334

The rifle is a Remi 700 XCR and I was using 215M's.

The load is technically over max and I am not going to shoot over book max I have decided but my question is why would you get that amount of variation between shots? Is RL22 reknowned for it? ALmost 100 fps is a lot between shots I would say. I am going back to the range on Monday but am going to work up from 62 grns upto 65 grns maximum.

Any ideas of velocity variation would be greatly appreciated.

Mny thanks

Are your speeds increaseing as you shoot each round? Maybe as the barrel heats up speeds go up.

Just a Wild guess...

There are only four shots here. Three of them are within "normal" parameters for shot-to-shot velocity variation. One is a little on the fast side, but is NOT statistically significant as one out of four samples! You really need to shoot a lot more rounds to see if there's a problem. The other three look pretty acceptable.

I have chronographed FACTORY ammo in which there was more than 100 FPS difference in MV in the same box.

another thing to pay attention to is muzzle blast . if the crono is close. i set mine up at around 15 to 18 feet from the muzzle.

If those are the shots in order, it looks like you are getting abit of a vel. increase as the chamber heats up. The other three are actually quite close.

Thanks all

I appreciate the feedback.

Yes the 4 shots were in that order and yes you are correct in terms of the first 3 are perfectly acceptable the 4th one is out a fair way. I did shoot them in relatively quick succession so it could well be that the 4th was as a result of things hotting up.

Thanks again

I think all the velocities look way high for the powder charge you're using. I shoot 66 RL22 with a 175 NP and this combo in Win brass goes 2901 fps. Mine is an old rifle probably has some throat wear and needs a bit more powder, but your 160 gr loads are registering 330 fps faster. I think you have a chrono problem, but I'd be scared if I got 3200 fps with a 160. side lighting without a chrony being shaded will cause such stuff by the way.

Those velocities would be near max for my STW.

jstevens

Very interesting in terms of the load you are using for your 175 NP's. I am getting quite pronounced extractor marks on the brass but the chrono didn't have its shades on. It was however an overcast dullish day with a 10 mph wind so I presumed that the shades were not required. Perhaps that could have at least threw the 4th shot out perhaps?

Anyway this week I will do some more testing and let you know of the outcome.

Ramrod

Yes they are upto STW velocities aren't they. I was always deliberating whether or not to get an STW and looks like I made my Rem Mag into one (not to be recommended obviously).

If you are starting out with a clean bore, it usually takes a few shots for the bore to get properly stabilized (fouled) for the readings to be significant. Your first half dozen shots should show an increase in velocity and then your shot to shot variations should start.

If you are getting pronounced extractor marks, blurred headstamps, and flattened primers, you are on thin ice.

Anymore I work up to where I see even the slightest casehead markings and back off 1 grain. Badly flattened primers usually come somewhat after you start seen ejector hole or slot markings on the case heads.

I have seen side lighting play havoc with a chrony. Some of my .223 loads that go 3100 fps were showing 3300 and my .338's with 210's 3090 fps. I had shot these loads for years and they chronographed 3080 fps and 2929 fps respectively. I don't think there is any way they are actually going 3200-3250 fps. Nonetheless if you are getting extractor marks, you are likely over 68-70000 psi.

Are you using Remington cases?

OK all

I have some embarrassing news.

I pulled the remaing 6 rounds that were unfired and the powder charge weighed 70.2 grns!!!

This is the first mistake I have made in 22 years of reloading. I cannot understand why because my beam scales showed 67 grns as they were left. The only thing I can put it down to was the fact that I threw each load from my harrel measure without weighing each one and when I went back to reload, the measure stuck and had to be disassembled to be cleaned etc. I can only think that perhaps it has thrown the weights incorrectly or something. The good thing is no damage done and a massive lesson learned.

I am weighing the charges individually on my electronic scales.

I went to the range yesterday and shot a .377 moa group with 66 grns of RL22 and it chronographed at 3016 fps (were it should be!) so I am very happy.

Anyway atleast there is no mystery any more.

Thanks for all your comments.

BTW Shootaway it is Winchester brass.

Hey Jon, You are one "LUCKY" fellow.

Sure glad you got it all figured out and did not create any scrap or need for bandages along the way.

Best of luck to you.

That sounds more like it. While 67 grains is a stout load with a 160 grain bullet, I couldn't see any way it would be much over 3000 fps, much less 3200. You got away with a mistake for sure, but everyone makes mistakes. According to shootaway you should certainly be ready for a new barrel.

I generally scale all loads using coarse grained powder.