Hornady vs. Sierra Data for .308

[MMH]

I am working up loads for my Rem 700 & Sig 716. I am loading up Hornady 180 gr. SST bullets with Federal 210 primers and Win .308 commercial brass. to a COAL of 2.74". and am at close to maximum loads per the Hornady manual. I have loaded up 40.0 gr. of IMR 4064, 41.7 gr. of Varget, 41.3 gr. of Win 748 and 41.8 gr. of BL-C(2). The primers are beginning to flatten a bit but do not llok too bad. The Sierra manual seems to allow heavier loads than the Hornady manual, but obviously is based on using Sierra bullets. As the primers look OK and I am within Sierra limits, can I slowly increase the loads? My objective is working up a long range hunting load, so I need accuracy & energy.

 

[MAT4-82]

I am working up loads for my Rem 700 & Sig 716. I am loading up Hornady 180 gr. SST bullets with Federal 210 primers and Win .308 commercial brass. to a COAL of 2.74". and am at close to maximum loads per the Hornady manual. I have loaded up 40.0 gr. of IMR 4064, 41.7 gr. of Varget, 41.3 gr. of Win 748 and 41.8 gr. of BL-C(2). The primers are beginning to flatten a bit but do not llok too bad. The Sierra manual seems to allow heavier loads than the Hornady manual, but obviously is based on using Sierra bullets. As the primers look OK and I am within Sierra limits, can I slowly increase the loads? My objective is working up a long range hunting load, so I need accuracy & energy.

Doesn't matter, They are all just guidelines. If you are seeing pressure signs stop and figure out what is going on.
You are talking about two very different rifles it is highly unlikely that the chambers are throated the same.
You will not likely get one load to be optimum in both.
A 180 being a bit longer your OAL suggests to me your projo is a ways back in the case likely causing a compressed load and combining that with jamming it in the lands you are going to have pressure.
I don't know if mag length is of concern for your purpose. That would change things also.
Work on one rifle at a time.
If mag length is not a factor measure your cartridge length to where the ogive meets the rifling.
I am guessing that the OAL you get will be a bit longer providing more room in the case and reducing pressure.
Hope this makes sense re: what you are experiencing

 

[MMH]

Doesn't matter, They are all just guidelines. If you are seeing pressure signs stop and figure out what is going on.
You are talking about two very different rifles it is highly unlikely that the chambers are throated the same.
You will not likely get one load to be optimum in both.

I have always been under the impression that just looking at a primer for signs of pressure is not reliable and that you can have high pressure w/ a flattened primer & cratered firing pin hole. I am apprehensive on exceeding recommended loads for that reason. On the other hand, I do not understand why one manual allows significantly heavier loads for the same bullet weight.

A 180 being a bit longer your OAL suggests to me your projo is a ways back in the case likely causing a compressed load and combining that with jamming it in the lands you are going to have pressure.

I loaded to a COAL as recommended by the Hornady manual. Unless, Sierra bullets contact the rifling significantly farther back than Hornady for the same weight (which I doubt), I don't see this as an issue. In addition, for all the powder weights, there seems to be significant empty case capacity where I do not see compressed charges as an issue.

I don't know if mag length is of concern for your purpose. That would change things also. Work on one rifle at a time.
If mag length is not a factor measure your cartridge length to where the ogive meets the rifling.
I am guessing that the OAL you get will be a bit longer providing more room in the case and reducing pressure.
Hope this makes sense re: what you are experiencing

Mag length is an issue. I can go to 2.8 on the AR10 & 2.9 on the 700. I am working up the loads "independently" for both rifles, just doing in parallel for the range sessions. I may seat the bullets a little further out after I measure my chambers, but will not be able to go much further out because of the magazine limitation.

Right now, I am not seeing pressure signs, but am not sure that I can safely increase loads. Question remains if I can go out to Sierra maximum loads w/ Hornady bullets.

 

[MAT4-82]

I have always been under the impression that just looking at a primer for signs of pressure is not reliable and that you can have high pressure w/ a flattened primer & cratered firing pin hole. I am apprehensive on exceeding recommended loads for that reason. On the other hand, I do not understand why one manual allows significantly heavier loads for the same bullet weight.


I loaded to a COAL as recommended by the Hornady manual. Unless, Sierra bullets contact the rifling significantly farther back than Hornady for the same weight (which I doubt), I don't see this as an issue. In addition, for all the powder weights, there seems to be significant empty case capacity where I do not see compressed charges as an issue.



Mag length is an issue. I can go to 2.8 on the AR10 & 2.9 on the 700. I am working up the loads "independently" for both rifles, just doing in parallel for the range sessions. I may seat the bullets a little further out after I measure my chambers, but will not be able to go much further out because of the magazine limitation.



Right now, I am not seeing pressure signs, but am not sure that I can safely increase loads. Question remains if I can go out to Sierra maximum loads w/ Hornady bullets.

To me primers starting to flatten is a pressure sign especially if the manufacturers data says I am near max.
The different manuals use data from totally different test subjects comprised of totally different mixes of components. What would surprise me is if they matched.


The Hornady SST has a secant ogive, Sierras are tangent ogive they will have different lengths for any given weight. I should not have said compressed charge, what I meant was reduction of case capacity.


Seating longer up to .060 on one and .160 on the other, short of engagement, should reduce the primer flattening


IMO no but if you decide to exceed the hornady data do so slowly. Like I said before though max loads are generally not the most accurate.
Good luck

 

[Pinecone]

Realize that not all primers are the same. Federal primers are known for having a softer cup. So you may see flattening primers with Federal, switch to CCI and no flattening with the same load.