Why such a big difference in 155gr .308 load data?

[Redhook]

I'm looking to work up a new load for my .308 using Lapua 155gr Scenar's. I have IMR 4895 that I was using for my 180gr SMK loads. Plus I have some H335 and Win 748 that I'll be testing as well.

When I cross check the Hodgdon load data with the Sierra load data the 4895 loads are significanly different. The Hodgdon starting loads are at where the Sierra Max Loads end.

Sierra Load Data
Sierra 155 SMK
IMR-4895
Start 39.8gr @ 2500fps
Max 43.7gr @ 2800fps

Hodgdon Load Data
Sierra 155 HPBT
IMR-4895
Start 43.5gr @ 2664fps
Max 47.5gr (compressed) @ 2897fps

If I cross check the H335 they are within a few tenths of a grain and the best I can do with the Win 748 is 150gr to 155gr and they are still pretty close.

So, I assume start with the Sierra spec and see where it leads me. Is anyone else loading 155gr's above 43.7 grains of 4895?

 

[Supersubes]

Re: Why such a big difference in 155gr .308 load data?

Generally speaking, Sierra has always been on the soft side for loads. In the dozen or so cals I have loaded for anyway.

I have been using hodgdon data exclusively as of late and It seems fine.

I use varget with 155's so I can't help you with 4895.

 

[Supersubes]

Re: Why such a big difference in 155gr .308 load data?

One more thing. Sierra maintains good control of their bullets, but has no control over powders and the resulting lot to lot consistency. This I feel is why they don't publish hot loads.

Hodgdon on the other hand can pretty much count on a Sierra bullet which is spot on.

Start low and do an OCW test.

 

[Redhook]

Re: Why such a big difference in 155gr .308 load data?

I don't know if it's just an issue of hot loads or not. The published velocities don't seem to jive either.

 

[Rob01]

Re: Why such a big difference in 155gr .308 load data?

Use the Hodgdon data unless you like really slow loads then use the Sierra. Example, Sierra lists 42grns as the max for a 175 SMK and Varget in the .308. 42grns is Hodgdon's starting load with 45grns being the max. Most people run around 44-44.5grns so you tell me which data you should use?

 

[KLambert05]

Re: Why such a big difference in 155gr .308 load data?

different books use different test rifles, you need to check barrel length, some tests use 22" barrel, and ive seen some that use 28". That can account for big differences right there. And sierra is a little on the conservative side with their rounds as well. Best way is just to load up some different loads and send them through the chronograph to get your actual muzzle velocity.

 

[Fuzzball]

Re: Why such a big difference in 155gr .308 load data?

"Why such a big difference in 155gr .308 load data?"

You won't have to look very long to find that's not unique to a 155 gr. .308 load. Bottom line, our safety lies in our own hands, not in a book.

 

[jdgray]

Re: Why such a big difference in 155gr .308 load data?

The Sierra data I have is all tested in Fed brass, which is on the heavy or lower volume side. Less powder makes more pressure in a smaller volume case. It depends what brass your using.....

 

[turbo54]

Re: Why such a big difference in 155gr .308 load data?

Sierras manual is conservative. Thats it.

All manuals are conservative ... we live in a litigious society. Truth be told, we're lucky we even have outfits making/selling us powder. If you have a last will/testament, consider stating to your heirs NOT to sue powder/firearm manufacturer in the event you taken out by a blown up gun. I dont need Hodgdon to go out of business because you put 45gr of titegroup into a 308 case instead of varget!

Shooting buddy of mine used to scoff at me charging over book numbers. We're both engineers and he went on and on about how hed NEVER go over book, because they have engineers researching/studying these things.

We'll he bought a new rifle and fired 1000 rounds trying to work up a load. Eventually, he realized the trend showed more powder = better. He settled at 46.5gr Varget with 175smk... shoots great. I really busted his balls good for going over book max! Then he explains how the casehead isnt growing, primers arent flat, bolt isnt sticking, no ejector marks.......same shit I tild him at the beginning of the season.

Don't be dumb.

 

[johnsobr]

Re: Why such a big difference in 155gr .308 load data?

Did you happen to accidently cross refrence imr 4895 with hodgdon H4895? Sounds dumb but they are different.

 

[Redhook]

Re: Why such a big difference in 155gr .308 load data?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: johnson5R</div><div class="ubbcode-body">Did you happen to accidently cross refrence imr 4895 with hodgdon H4895? Sounds dumb but they are different.</div></div>

Nah. It's IMR to IMR.

Everyone so far has had a valid claim, but it still sends up a red flag when the numbers are so far apart. I could accept some overlap. Especially when other loads combinations are within a few tenths.

But my goal is to load accurate ammo and NOT detonate my gun, harm, or kill, myself or others. Regardless of what some engineer or lawyer swears to.

 

[KIDGLOCK]

Re: Why such a big difference in 155gr .308 load data?

Its all VooDoo and Debil worship .

Bottom line, start low and work up till you get the bad signs , flat primers,extractor marks etc.

 

[Supersubes]

Re: Why such a big difference in 155gr .308 load data?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Redhook</div><div class="ubbcode-body"> <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: johnson5R</div><div class="ubbcode-body">Did you happen to accidently cross refrence imr 4895 with hodgdon H4895? Sounds dumb but they are different.</div></div>

Nah. It's IMR to IMR.

Everyone so far has had a valid claim, but it still sends up a red flag when the numbers are so far apart. I could accept some overlap. Especially when other loads combinations are within a few tenths.

But my goal is to load accurate ammo and NOT detonate my gun, harm, or kill, myself or others. Regardless of what some engineer or lawyer swears to. </div></div>

Do you have any issues with reading pressure signs? If you do, please ask. Look in the loading section here, you'll find a huge variance in loads and resulting velocities.

Use the hodgdon data, use their starting load, and work up. It really is that simple.