308 load questions

[coffeediver]

Back in May I asked a question on why my 308 loads were much faster than the reload data would say it should be. I was loading Lapua brass, 43.3 grains of Varget, CCI BR2 primers and 175gr SMK bullets. These loads were going about 2750fps when Hodgdon website says that 45 grains should be about 2690.

There was some question on case capacity on the Lapua brass. I went through some more testing and have since changed the load to 42.6 grains and using Federal GM 210 primers. These round have dropped in velocity and average 2707fps. I have since gotten Quickload and measured the case capacity. Putting all values in and per Quickload, these rounds should be about 2600fps.

Not getting extractor marks, but am getting flattened primers.

What am I missing.

Barry

 

[Doug Beach]

Some barrels are faster / slower than others. Some lots of powder are faster / slower than advertised.
Some batches of primers are hotter / cooler than others.
Some chronographs are not particularly precise.
I’m not trying to be a smartass, but there are many, many variables. Your predicted velocity is off by 4%. Not that much, in the scheme of things.
How does it shoot?

 

[JB10]

Thats some good speed. Im using imr4064 at 44.5 grains. I single load and got the bullet touching lands. 175gr berger vld hunting. Its a Remington 700 with a 26 inch tube and only going 2,673fps

 

[Straightshooter1]

Back in May I asked a question on why my 308 loads were much faster than the reload data would say it should be. I was loading Lapua brass, 43.3 grains of Varget, CCI BR2 primers and 175gr SMK bullets. These loads were going about 2750fps when Hodgdon website says that 45 grains should be about 2690.

There was some question on case capacity on the Lapua brass. I went through some more testing and have since changed the load to 42.6 grains and using Federal GM 210 primers. These round have dropped in velocity and average 2707fps. I have since gotten Quickload and measured the case capacity. Putting all values in and per Quickload, these rounds should be about 2600fps.

Not getting extractor marks, but am getting flattened primers.

What am I missing.

Barry

As mentioned in previous posts (even those going back to May), there are various things that can be at work here, some of which may together be adding up. BUT . . . I strongly feel that your chrono is likely the major culprit in getting such high readings, and it should be easy enough to check out by using someone else's to see what kind of readings you get. Until you can verify your chrono's accuracy you it's going to be difficult to find what other factors might be at work also.

 

[Ned Ludd]

Back in May I asked a question on why my 308 loads were much faster than the reload data would say it should be. I was loading Lapua brass, 43.3 grains of Varget, CCI BR2 primers and 175gr SMK bullets. These loads were going about 2750fps when Hodgdon website says that 45 grains should be about 2690.

There was some question on case capacity on the Lapua brass. I went through some more testing and have since changed the load to 42.6 grains and using Federal GM 210 primers. These round have dropped in velocity and average 2707fps. I have since gotten Quickload and measured the case capacity. Putting all values in and per Quickload, these rounds should be about 2600fps.

Not getting extractor marks, but am getting flattened primers.

What am I missing.

Barry

Were you getting flattened primers with the previous 2750 fps load? One reason could be the hardness of the primer cup. I believe the cup thickness of Fed 210s and CCI BR2s is the same, but the BR2 cups might possibly be a bit harder.

One thing you have to be aware of is that online reloading sites and/or reloading manuals are estimates only. Their values are not written in stone. They have no way of knowing your freebore length, COAL, case volume, type/brand of primer you're using, how fast your specific Lot of powder is, how fast your specific barrel is, etc. They typically only define COAL, powder type, charge weight, bullet weight, and barrel length, nothing else. Any differences between your setup specifics and their test setups will necessarily generate different pressure/velocity values. Further, observational pressure signs such as flattened primers and hard bolt lifts are only crude estimates at best, and their interpretation can easily differ between individuals.

According to the numbers you provided above, your velocity dropped an average of 43 fps with a reduction in charge weight of 0.7 gr, which comes out to a tad over 6 fps per 0.1 gr. That is well within the range I would expect per 0.1 gr charge weight decrease in a .308 Win case. Have you re-calibrated your QuickLoad file to more accurately represent the new load? In other words, have you readjusted the charge weight and temperature (and any other parameters that might have changed),then adjusted burn rate (Ba) until the predicted velocity output provided by QL was 2707 fps? If yes, what was the predicted pressure for the new load? If no, it would be worth doing, if for no other reason than peace of mind if the load is predicted to be well under MAX pressure. If that turned out to be the case, it might be worth switching back to the BR2 primers with the reduced charge weight and see what kind of velocity you get, as well as how the primers appear after firing. I'm not certain how the brisance of the two primers compares, but if the velocity at 42.6 gr powder with BR2s is similar to that with Fed 210s, the "flattened primers" go away, and QuickLoad predicts a pressure well below MAX for the load, I think it's safe to say there's likely to be some difference in the primer cup hardness.

 

[msinc]

Is there a difference in the length of the barrels between the published reloading data test rifle and yours???? Many 308 loads are tested with 22" barrels {M1A. AR-10...} none of my 308's are less than 28".

 

[coffeediver]

As mentioned in previous posts (even those going back to May), there are various things that can be at work here, some of which may together be adding up. BUT . . . I strongly feel that your chrono is likely the major culprit in getting such high readings, and it should be easy enough to check out by using someone else's to see what kind of readings you get. Until you can verify your chrono's accuracy you it's going to be difficult to find what other factors might be at work also.

The original loads at 2750 were done over a Caldwell Chrony. The new ones are on a magneto speed.

 

[coffeediver]

Is there a difference in the length of the barrels between the published reloading data test rifle and yours???? Many 308 loads are tested with 22" barrels {M1A. AR-10...} none of my 308's are less than 28".

Hodgdon lists,
Case: Winchester
Twist: 1:12.000"
Primer: Federal 210M, Large Rifle Match
Barrel Length: 24.000"
Trim Length: 2.005"

Mine is also a 24" barrel but I am shooting with a can and I also trim to 2.005 but barrel twist in 1:10.

 

[coffeediver]

Were you getting flattened primers with the previous 2750 fps load? One reason could be the hardness of the primer cup. I believe the cup thickness of Fed 210s and CCI BR2s is the same, but the BR2 cups might possibly be a bit harder.

One thing you have to be aware of is that online reloading sites and/or reloading manuals are estimates only. Their values are not written in stone. They have no way of knowing your freebore length, COAL, case volume, type/brand of primer you're using, how fast your specific Lot of powder is, how fast your specific barrel is, etc. They typically only define COAL, powder type, charge weight, bullet weight, and barrel length, nothing else. Any differences between your setup specifics and their test setups will necessarily generate different pressure/velocity values. Further, observational pressure signs such as flattened primers and hard bolt lifts are only crude estimates at best, and their interpretation can easily differ between individuals.

According to the numbers you provided above, your velocity dropped an average of 43 fps with a reduction in charge weight of 0.7 gr, which comes out to a tad over 6 fps per 0.1 gr. That is well within the range I would expect per 0.1 gr charge weight decrease in a .308 Win case. Have you re-calibrated your QuickLoad file to more accurately represent the new load? In other words, have you readjusted the charge weight and temperature (and any other parameters that might have changed),then adjusted burn rate (Ba) until the predicted velocity output provided by QL was 2707 fps? If yes, what was the predicted pressure for the new load? If no, it would be worth doing, if for no other reason than peace of mind if the load is predicted to be well under MAX pressure. If that turned out to be the case, it might be worth switching back to the BR2 primers with the reduced charge weight and see what kind of velocity you get, as well as how the primers appear after firing. I'm not certain how the brisance of the two primers compares, but if the velocity at 42.6 gr powder with BR2s is similar to that with Fed 210s, the "flattened primers" go away, and QuickLoad predicts a pressure well below MAX for the load, I think it's safe to say there's likely to be some difference in the primer cup hardness.

No, I don't remember the primers being flattened this much but I was getting extractor marks. Unfortunately I do not have any CCI BR2 primers left or I would test that hypothesis.

I have more testing to do but winter in Colorado can be challenging to say the least. I may have to just adjust my loads to speeds that are consistent with accuracy and be happy. These loads did get me a .312" 5 shot group at 100yrds all at the same elevation, just walking left to right a bit, others were no larger than .6" with a flyer.

 

[msinc]

Well, I would say that "listed" and actual are two different things and they can be pretty different...back in the 70's Remington listed the 130 grain Bronze Point ammo for a 270 at 3150mv.....that particular powder {whatever it is} was never available to the public!!!!

 

[rr2030]

The only load I use for my .308 is almost exactly what yours is, mine being 44.0 Varget, CCI-BR2, 175TMK, Lapua Brass. I see 2600 fps.

Chronographs, component lots, air density, barrel length, etc all play a part. I learned a long time ago, create the best grouping round for your rifle, then for the sake of generating ballistic data check the velocity.

FWIW: I have used Federal, Black Hills, Lapua and Winchester brass, Fed GN210, CCI BR-2 primers, 175 SMK and TMK. Against popular opinion, any combination of these components give the same result, not supposed to, but lucky me, they do.