200 fps faster than starting load?

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brybenn

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I'm wondering if anyone else has had a starting load surprisingly faster than listed?
I'm using lee book 2nd ed and lee paper that came with the dies. Starting load is 72 gr H4895 max and 77 grs for 2349 fps max with a 400 gr bullet. However I'm getting 2420-2425-2419-2422-2430 fps from just 72 grs powder with woodlieghs and 2399-2420 fps with Remington flat nose soft points 15' in front of the muzzle

Primers are win large rifle
Brass is ww trimmed to length
Powder 72 gr H4895
Gun Mauser 98 26" barrel 458 wm

Primers still have a slightly rounded edge. Extraction is easy

Could the longer barrel alone account for the extra velocity?

Also 70 gr of h4895 under a 500 gr bullet gave 2200 fps even. Starting load as well

My scale is calibrated and my other loads from other guns matched velocity of other chornos from other days when shot over mine
 
I'm sure someone more knowledge able will chime in soon but I know that if you're using a longer barrel than the one the original load was developed with you will get higher velocities. I think it's about 75 fps/inch of barrel. So if the barrel that load was tested with was a 24" inch barrel, it's not a far stretch to see you getting 200fps more in you're using a 26" barrel. Also consider your crony velocity variability as well.
 
Typically I got 15-30 ft/sec per inch of barrel when I tested and measured.

Brass capacity could be less, bullet seated differently, tight chamber, could be a ton of things.

If you have a known chorographed load run that through see if numbers are still good.

I would back of 5grains maybe.

More pressure has to come from somewhere if your measurements on the velocity are accurate.
 
Ran into a similar situation with one of my 308 Norma Magnums.

I have always been able to reach 3100 fps in a 24" 308NM with 75/76 grains of Norma MRP [always start a new rifle at 73 grains]

Imagine my surprise to see my starting load in this rifle graph 3160!!
I am now using 72.5 grains to achieve what it takes 2.5 - 3.5 grains more to get in my others.

Always start low with an unknown rifle. Murphy is alive an well. :)

Dave.
 
I see it once in a while. It happens more often with a tight chambered, short throat, match grade barrel. I've got a couple here that meet or exceed the velocity of the top load with the starting load or a grain more. As far as I'm concerned, that isn't a problem. If anything it just shows why there are starting loads.

Usually if I search enough manuals I can find one that agrees with what the rifle and chronograph are telling me or comes close. Same thing when a rifle swallows an extra grain or two of powder.
 
BB..........sounds to me like your 458 is a semi custom job with a 26" barrel and 98 action, so it would be logical to assume that the person doing the smithing cut a nice tight clean chamber as opposed to a sloppy factory one designed to accept any ammo, even covered in mud.............add this to the 26" tube and you will get a few extra fps. Makes perfect sense to me...........
 
When I was testing hot .45-70 loads in my modern 32" barreled single shot, I noticed marked increases over the loads in the book that were fired through a 24" barrel. I was mostly using full loads of IMR 3031 and a 300 grain bullet I was getting around 2500 fps, 400 fps above the highest velocity in the book. None of the other loads i tested had that margin of velocity increase. So sometimes the components and the firearm just come together and work better than expected. Whether it's the powder working well with the barrel length, a perfect chamber, the right bullet and crimp etc... sure is sweet when it works out. I did double check the crony with some known velocity rounds.
 
c-fbmi said:
BB..........sounds to me like your 458 is a semi custom job with a 26" barrel and 98 action, so it would be logical to assume that the person doing the smithing cut a nice tight clean chamber as opposed to a sloppy factory one designed to accept any ammo, even covered in mud.............add this to the 26" tube and you will get a few extra fps. Makes perfect sense to me...........
Click to expand...

Yes it's a semi custom gun. Interarms mark X 98 action with a 26" barrel with really nice express rear sights and front ramp post. Full barrel and action and floor plate metal glass bedded. Custom wood stock. It was a personal moose gun of a local gunsmith. His work is absolutely amazing. Very talented. Good to know that's its fairly common. I loaded up another 40 rounds to shoot this weekend.
 
Eagleye said:
Ran into a similar situation with one of my 308 Norma Magnums.

I have always been able to reach 3100 fps in a 24" 308NM with 75/76 grains of Norma MRP [always start a new rifle at 73 grains]

Imagine my surprise to see my starting load in this rifle graph 3160!!
I am now using 72.5 grains to achieve what it takes 2.5 - 3.5 grains more to get in my others.

Always start low with an unknown rifle. Murphy is alive an well. :)

Dave.
Click to expand...

Was that the P17 rifle in 308NM I sold it to you a while ago?
That barrel wasn't factory one IIRC and the max load and most accurate one was 72gr of rl22 with 180gr Hornady IL.
Sure we tried up to 74 gr of rl22 but accuracy diminished and brass showed some straining and you don't need any "suprises" while hunting....
 
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