What could be the cause of this?

[ssteve]

Worked up a load for my AR for varmints recently. Shooting 25.0gr of varget, lake city brass, nosler 77gr bthp and cci 400's. Its a compressed charge and over recomended max but I get no pressure signs at normal temps and only the occasional swipe when its real hot out. The barrel is a Centurion Arms, crane spec mk12 barrel.

I was getting 2740 fps with an sd of about 8-10 over the last 50 rounds or so. I normally shoot 10rnds over the magneto speed before I start shooting just to see where it sits on that day and if the first round will have a significant drop in velocity.

So I recently ran low on cci 400's and the local shop doesn't have any so I figured I would try out some primers. For each of them I loaded up 25 rounds at 25.0gr of varget, shot a group of 15 with the magneto speed on and then two 5 round groups. Let the gun cool for 10 min and then repeated the same.

first was remington 7 1/2's:
ave 2705
sd 15
extreme spread I believe was around 30

then winchester wsr's.(heres where the issue is)
ave 2810
SD 221!!!!
low: 2658
HIGH: 3268 & 3276!!!!!!!!!!!!!!!!
of the other 13 shots everything else was about 2700. I pulled those three and sd was about 18 with an extreme spread of around 30.
Those two cases showed zero pressure signs as well as they shot dead center in the group of 15. I inspected the gun, no issues, didn't sound odd or feel odd. No real explanation for it. On top of everything 25gr is already slightly compressed, I highly doubt I could get enough varget in the case to come anywhere near 3200fps

went on to shoot cci 400's in the same fashion:
ave 2744
sd 11
extreme spread around 28

then cci 450's
ave 2716
sd 10
extreme spread around 22

All 5 round groups were sub moa, nothing looked odd in any of it with how it printed on paper.

The only thing I can think is that there was an issue with the magnetospeed... Maybe loose?

I also ran the same charge behind some 73gr eld-m's and cci 400's and 450's. very similar results but velocity was up about 30fps.

 

[winniedonkey]

Did you change the intensity level at all? I've had those crazy random numbers before due to it being too strong.

 

[ssteve]

Did you change the intensity level at all? I've had those crazy random numbers before due to it being too strong.

Nope, never changed the setting and this was in the middle of a 15rnd string.

 

[Xander3Zero]

Interesting this came up, I was doing some load development the other day with a Magnetospeed and had a "2850" velocity reported during some loads that were averaging around 2700. I am pretty carefully weighing charges to 0.1gr with a beam scale and trickler, and for me to go from 2700 fps to 2850 is about ~1.8gr difference (for a 223 rem with varget), so I am really not sure what could have caused that outlier in my data.

 

[Greg Langelius *]

Winchester primers have among the highest degrees of brisance (layman English - flash), and are primarily intended for use with Winchester ball powders, which are spherical with a more resistant coating, and require a more positive ignition source. Some of that extra velocity, etc., may be related to the primers.

I use Winchester primers for hunting loads, Garand loads, and lighter practice loads, where I want a more definite ignition feature, especially for cold weather.

Combining a hotter primer with an over max load is simply going to put you outside the normal envelope of reasonable expectations; and then there's the safety aspect, too.

First, stop using Winchester primers for this application. Second, redevelop the load to the next lower velocity node. Your rifle will thank you.

I use Varget for my .223/5.56 loads. My top loads for HDY 75gr HPBT Match bullets are between 23.5gr and 24.0gr. Bullets in this weight range may or may not be the most suitable for the Varmint application.

Gelatin testing with IMI 77gr showed explosive expansion at about 6" of penetration, which is about 2" beyond the distance where it emerges with a through and through on a Marmot/'Chuck. For what you're trying to do the current Midway sale on IMI 77gr may be helpful, but I don't see the load as being appropriate for such small game. It's good for longer distances, but needs a lot more meat in which to complete its expansion.

I tend to use 50-55gr bullets for Varmints, with a specific Varmint designation. For 50-55gr bullets in the AR, I use a max load of 26.0gr. If your varmint application requires shooting distances beyond 300yd, consider the .22-250 (50gr Nosler BT/36.0gr Varget - max load).

Greg

 

[ssteve]

Winchester primers have among the highest degrees of brisance (layman English - flash), and are primarily intended for use with Winchester ball powders, which are spherical with a more resistant coating, and require a more positive ignition source. Some of that extra velocity, etc., may be related to the primers.

I use Winchester primers for hunting loads, Garand loads, and lighter practice loads, where I want a more definite ignition feature, especially for cold weather.

Combining a hotter primer with an over max load is simply going to put you outside the normal envelope of reasonable expectations; and then there's the safety aspect, too.

First, stop using Winchester primers for this application. Second, redevelop the load to the next lower velocity node. Your rifle will thank you.

I use Varget for my .223/5.56 loads. My top loads for HDY 75gr HPBT Match bullets are between 23.5gr and 24.0gr. Bullets in this weight range may or may not be the most suitable for the Varmint application.

Gelatin testing with IMI 77gr showed explosive expansion at about 6" of penetration, which is about 2" beyond the distance where it emerges with a through and through on a Marmot/'Chuck. For what you're trying to do the current Midway sale on IMI 77gr may be helpful, but I don't see the load as being appropriate for such small game. It's good for longer distances, but needs a lot more meat in which to complete its expansion.

I tend to use 50-55gr bullets for Varmints, with a specific Varmint designation. For 50-55gr bullets in the AR, I use a max load of 26.0gr. If your varmint application requires shooting distances beyond 300yd, consider the .22-250 (50gr Nosler BT/36.0gr Varget - max load).

Greg

Thanks for the info. There was a node around 23.8-24.0 and only about 60-80fps less so I will just back down to 24.0 and call it good.

As far as rounds good for varmints, I am not really overly concerned with saving the pelts on the coyotes and this barrel doesn't particularly shoot much of the lighter stuff very well. I've been able to get some 62-65gr stuff to be ok but nothing under that. It shoots all the heavy stuff great though. it really really likes the 70gr tsx stuff but that stuff is far too expensive to be shooting squirrels and dogs with but I have a solid load with ramshot tac that I will be using for deer.

 

[Greg Langelius *]

OK, I misread you, thinking P-Dogs and 'Chucks, when what you meant was Coyotes. I call them Predators. The 77's just may be a good round for them.

I repeat that the Midway sale on IMI 77 is probably a good idea for you. I'm going to try three boxes myself, but for MR paper applications. I took recent delivery of six boxes the new Hornady/Frontier 75gr HPBT-Match, which is loaded at Lake City using Frontier stamped LC brass.

I'll be testing a number of MR loads in the coming weeks.

Greg

 

[ssteve]

OK, I misread you, thinking P-Dogs and 'Chucks, when what you meant was Coyotes. I call them Predators. The 77's just may be a good round for them.

I repeat that the Midway sale on IMI 77 is probably a good idea for you. I'm going to try three boxes myself, but for MR paper applications.

Greg

Sorry I kind of subcouncisly group all the garbage animals into the varmint catagory. I think I am going to stick with the 73gr eld's cause they seem to buck the wind a little better and drop less. At least thats the case to 300yrds which is as far as I have been able to take them out to.

 

[McCrazy]

Barrel harmonics being what they are, I have a hard time believing 2 rounds going 500 fps faster than your other rounds would stack up in the same group. I also wouldn't expect them to show no pressure signs nor cause no damage to your rifle.

These 2 factors make me think you probably just had a reading error with the magnetospeed.

 

[winniedonkey]

Nope, never changed the setting and this was in the middle of a 15rnd string.

Yea that shit happens. I just drop those from the data.