Home Forums Hunting & Shooting Long Range Hunting barrel fouling or temperature

I was confirming I had found my load again since the Hodgdon takeover from IMR. Went with a clean bore 7/300 win mag 140 ABs Old load was 77.5 new load is 78.1?
71 degrees
1st shot 3350
2nd shot 3435
3rd shot 3495

No signs of pressure other than slightly flattened primers. The killer is that all 3 shots were no more than .3" from center but were over a 2.0 " spread vertically
What would be your assesment of the cause of such a deviation?
Started with clean bore and I didnt have time but for 3 shots when allowing for bbl cool down. Is 7828 that temperature sensative? I had some deviation with the old load but it was in the 30-40 fps range. I will get back and do some checking when I get some time ,but I was want yall's opinion. Thanks
Steve Eggers

I know nothing of the 7/300 win mag 140ABs. In fact, I'm not even sure what that is. It looks like a 7mm bullet in a 300 Win Mag. Is 78.1gr a max load? And please don't rely only on "pressure signs," they lie.

So, 3 shots is all you got? That's very little data to go on, but the spread is pretty bad at 145. You need to tell us how you load powder, because that would be the first place I would look.

The first shot or two out of a clean bore is always slower according to my chrono data. Enough so I won't hunt or compete with a clean bore.

When switching bullet jacket types and or powder types I"ve also seen on occasion impact variances that don't settle down again until a few shots are downrange.

I don't take data to mean anything basically until I"ve shot 10 rounds down the tube of that ammo, then I'll shoot for data and trust enough data.

You gotta shoot some foulers.

Thanks for the responses
For those that dont know the 7/300 is a 300 Win necked to 7 mm
and there is no published data that I am aware of . When I first got it I ran it up till I saw signs such as shearing brass off the base and stickey bolt lifts .
These loads are as easy to bolt firing formed rounds as factory's are .
I have had this rifle for several years and it never before has shown this much differance between fouling shots.
I have a chance to go now to do some more checking , It's a little cooler today so we will see. The only differances are the temp and a clean bbl from when I developed loads a couple weeks ago
I will update
Steve Eggers

Steve-I shoot the 7 Mashburn Super quite a bit and I've used 7828 for the most part. In my brief tests I've not found it to be temp sensitive at all.

Here's what I'd do, I'd take the exact 3 cases and run them again and see what they clock. If I see something once I wonder, if I see something 2x I go hmm but if I see things 3x then I feel I can make a decision about it.

It'd be interesting to find out if the first shot out of your clean bore is typically the slow one or not?

Best of luck to ya

Dober

Side note, it strikes me as 77-78 grains of 7828 with a 140 would be a pretty toasty load for a 7/300 WM?

Very common for spread not to settle until the bore is fouled a bit.

Like Jeff, I also foul when switching bullets or powders as it gives a similar effect.

I've used 7828 in the 7x300 wtby of mine, it was not temp sensitive.

But as noted, the first round out of a clean barrel is almost always slow and on the order of 100 fps in my experience. And it can take like 5 fouling rounds or so before any chrono data is somewhat reliable.

Have you weighed those 3 cases? Dober might be onto something, maybe its a case capcity issue?

Just got back from the range and the temp wasnt a problem it was the fouling . didnt clean and shot 3 more shots --1 I didnt have my crono up and 2 were 3485 - 3491 add that to my last shpt yesterday of 3495 and that just aint too bad. Hard to beleive a change in powder and brass (Lapua to Winchester) would allow you to gain 100 fps with no apparent change in pressure didnt measure the group but it was around .5 - .6 @ 100 with a 15 - 20 wind


Dober--- There were 4 of these rifles built at the same time with the same specs I know at least 1 other that showed the same signs as me at about the same load with the Lapua brass.
I am getting more powder more speed with the win brass-- I havent weighed for comparison, but I will tonight I suspect the win brass is lighter

you don't ever gain speed without gaining pressure unless its going to a different powder, case capacity, bullet coating etc.....

Lapua weighs 277.3 with spent primer and Win weighs 220.5 with same
Win is lighter by 56.8 gr

I have never fooled with case weight and capacity by weighing
Does anyone have any idea if this much differance in weight could mean that much differance in Max powder charge?

Anybody know the difference in case capacity between the 7/300 and 7 Mashburn?

Steve I'd say that 56.8 is a big time jump and I'd certainly bet on the heavier one going a lot faster. Probably too fast in that case.

Dober

56.8gr difference with the same cartridge? Is that even possible using the same materials?

Yep, that difference is possible. I"ve seen it before it big mag cases hence my questioning.

A difference of 20ish grains almost 30 IIRC in a 257 wtby, meant drop the charge by 1.5 grains to have the same velocity.

Ran over to Hagel's data on the Mashburn (I have not worked 140's in The cartridge). He shows a max of 76-7828-140 Partition for 3455 from a 28" barrel, and 3375 for the same load with a 24" tube.

I doubt there is much capacity difference between the cases.

You are looking at almost 20%! That will make a huge difference. No way you can get the same performance from the same load with those two figures. That's almost like changing powders and expecting the same group. I would never have thought that two brands of brass would vary that much. The Lapua must be a lot thicker in the web, maybe some all the way thru, although you can only go so thick in the neck. When I bought my 6.5-06AI last year, it came with some fireformed Win. 25-06. I started my load workup with them and lost several with loose primer pockets and a couple head seperations, in only a couple uses. The pressure snuck up on me very quickly, this being my first Ackley. I found some R-P brass, it weighs about 6gr more, and I haven't had a loose pocket since. Due to this, I assume most of the difference is in the web. More capacity, more powder; in effect, more cartridge and more speed.

SteveE,

Without firing more rounds from a fouled barrel, we're all just guessing what the problem is. IMO, you need to get that barrel fouled and keep it there while testing. I doubt it's the Lapua brass. The quality is just too good to have such a large swing in fps. Something I can get away with in the dry climate of Utah is not cleaning barrels. Since I my use of Ultra Bore Coat I have several rifles that don't copper foul and keep their accuracy. My competition sniper/tactical rifle in 6.5x47 has not been clean in over 1000 rds and still shoots 1/2 MOA 5-shot groups. You might try letting your barrel stay fouled (ok, I'll say it; "dirty") through out your load development.

Alan

Started with clean bore and I didnt have time but for 3 shots when allowing for bbl cool down. Is 7828 that temperature sensative? I had some deviation with the old load but it was in the 30-40 fps range. I will get back and do some checking when I get some time ,but I was want yall's opinion.