Odd rang results with the 8MM Mag

Greg Nolan

Handloader
Nov 25, 2004
2,143
18
Today I took the 8MM Rem Mag to the range today to start prelim velocity and pressure checks. Ammoguide had loads for 200 gr bullets with a max of 88 grs. of Reloder 25. I started with new Rem brass CCI 250 primers and a load of 86 grs. OAL was 3.6 " and used a 200 gr A/B.
I loaded three groups of three at 86, 87 and 88 grs. I marked the bullets of each group with the powder weight. I measured each load individually and verified the OAL with a micromiter on each cartridge.
Here are the results:
86 grs. = 3031-3034-3038 Nice consistancy and about the velocity I expected.

87 grs. = 3390-3401-3356 Pressure looked the same as 86 grs but the velocity is unreal looking.

88 grs. = 3284-3290 and one didn't read . If I hadn't been so carefull about seperating and marking the loads it would seem 87 and 88 are reversed.
All the charges are compressed and it's a 24" barrel. I don't remember ever seeing a drop in velocity with a bigger charge of powder. Is there any pressure anomily that could do that?
I've reloaded another group of 87 and 88 gr loads to re check with but I'm puzzled. :roll: I Spoke with some very knowedgable folks at the range and they verified my pressures didn't look bad in fact all 3 looked about the same. Easy extraction of the bolt and case. The Chrony was about 12 or so feet from the muzzle.
 
Yes, I've seen it before. What you described will happen from time to time with slow burning powders, and RL25 is a really slow burning powder. If you had a longer barrel you would of probably seen a velocity increase, instead of a decrease on your last load. You have reached the plateau. If you wish to increase velocity further, you will need either a faster powder, or a longer barrel.
 
Greg,

The law of diminishing returns! Reshoot the loads and if the results are the same, you will need to change powders or get a longer barrel. The results with 87.0 grs is impressive!
You might also want to put a new battery in your chronograph.

JD338
 
Greg,

I would have predicted that the load was about right for that cartridge. You should have had complete combustion, even in a 24 inch barrel. However, the results speak of maxing out on the charge. This is not an unusual observation with slow powders. Tell us what you observe on the second set you shoot.
 
Greg Nolan":354ue0i5 said:
Today I took the 8MM Rem Mag to the range today to start prelim velocity and pressure checks. Ammoguide had loads for 200 gr bullets with a max of 88 grs. of Reloder 25. I started with new Rem brass CCI 250 primers and a load of 86 grs. OAL was 3.6 " and used a 200 gr A/B.
I loaded three groups of three at 86, 87 and 88 grs. I marked the bullets of each group with the powder weight. I measured each load individually and verified the OAL with a micromiter on each cartridge.
Here are the results:
86 grs. = 3031-3034-3038 Nice consistancy and about the velocity I expected.

87 grs. = 3390-3401-3356 Pressure looked the same as 86 grs but the velocity is unreal looking.

88 grs. = 3284-3290 and one didn't read . If I hadn't been so carefull about seperating and marking the loads it would seem 87 and 88 are reversed.
All the charges are compressed and it's a 24" barrel. I don't remember ever seeing a drop in velocity with a bigger charge of powder. Is there any pressure anomily that could do that?
I've reloaded another group of 87 and 88 gr loads to re check with but I'm puzzled. :roll: I Spoke with some very knowedgable folks at the range and they verified my pressures didn't look bad in fact all 3 looked about the same. Easy extraction of the bolt and case. The Chrony was about 12 or so feet from the muzzle.

I agree the 2nd and 3rd velocites look very unreal. 350 extra fps with 1 grain powder increase and 250 extra fps with 2 grain increase. I would try them again with a fresh battery in the chrono. Did the sky conditions change between the 1st and 2nd/3rd shot strings? Did the sun come out through a cloud between the 1st and 2nd/3rd? Even with shy screens the sun will cast a shadow and if so that can cause misreading on a chrono.
Just my .02
 
Barrel length has little or nothing to do with complete powder burn. If the powder's going to burn, it will happen in the first few inches of bullet travel. If the burn is incomplete, it's because sufficient pressure is not maintained long enough for the powder to all undergo reaction. A hotter primer could help, as could a heavier bullet, or maybe even seating closer to the lands.

I have also experienced velocity decreases with increased powder charge. My guess is that a hotter primer would have negated that effect somewhat, but maybe it's a good thing I didn't try it. I am pretty sure I was attempting to push TOO hard.
 
Repeat the test and report. Something is not right.
 
Sorry Riverrider, but my extensive chronograph experience contridicts your statements.

A good example is H4831 with a 130gr bullet in a .270 Winchesters.
Velocity will max out in a 22" bbl at about 59.5 gr, but velocity will continue to increase all the way up to 62gr of powder in a 26" barrel.
 
I repeated the test today with absolute precision.
2 problems:
The Chrony was probably not fully open. The tripod has a lip that I noticed today that held it slightly open making the distance between the two sensors shorter and the velocities read high. Fixed that!
The velocities today were:
87 grs.= 3033-3038-3030
88 grs.= 3123-3083-3114
It sure looks like I had the loads reversed unless the wind was playing with the partially open Chrony. But I think the problem was me.
As another question , do you think the extreem spread of 40 fps for 88 grs is enough to effect shooting out to 500 yds for hunting purposes or should I drop to the 87 grs. with the extreem spread of 8 fps?
 
Greg,

Personally, I'm more focused on the standard deviation than I am on extreme spread. I arbitrarily set a one percent SD for my loads. There are sometimes surprises, but in general this keeps me honest.
 
I would go with which ever one is the most accurate, speed is nice but accuracy kills. 100fps isn't going to really make much difference. Plug your data into a ballastic calc and see what little difference in drop at 500 yards there is between the 87 and 88 grain ave vel.http://biggameinfo.com/
 
Much better results. I would use the most accurate load.
 
Greg,

First off, glad you fixed the problem.

Based off your last range results, I would go with the 87.0 load and the ES 8.
I would reshoot the 87.0 and 88.0 gr loads, also try 87.5 grs and compare the differences.
OU812 said it best, "Go with which ever one is the most accurate, speed is nice but accuracy kills".
What kind of accuracy are you getting?
You are almost there. :wink:

JD338
 
Jim,
I don't have a clue about the accuracy :oops: I just changed scopes to a 4-12x40 and was just working up the velocity and extreeme spread. Next will be accuracy including overall length variations.
I did go with the 87 grs. for the next 10 shots to see if I may already have a shooter. If nothing else I do have a KICKER :shock: I put one of the new factory LSS pepper laminate stocks on it and it feel real good. The new ones are more of a semi-gloss but I like it
I'm thinking that if this shoots good I may just leave it an 8MM. It's a good inbetween caliber with 4100 to 4300 FPE. It's between the 300 and 338 RUMs. It WILL get a muzzle break though :wink:
Greg
 
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