I ran into a bit of an interesting Quandry this week. I'd loaded for 3 different 270 WSM's and all shot very well with 140gr Accubonds and 66grs of RL-22. I Chrono'd the Kimbers with this load at a little over 3200fps.
I bought a new Sako 85 in 270 WSM and naturally wanted to try the same load in it. It shot accurately but when I got around to chronographing it (after loading 100rds of it!) it was 150fps slower than it was in the Kimbers. It was only about 3075fps! Pretty sure I'm using the same lot of RL-22 and it is the same lot of 140gr Accubonds.
The Sako has a good deal longer throat than the Kimbers. I'm pretty sure it's longer than standard. Do you think the difference in Throating could cause this much velocity difference? Do Sako's maybe have a little bit larger bore diameter?
I noticed the same thing in a Sako M-75 Finnlite in 300 WSM. A Max powder charge of Magpro gives only about 2925fps with an 180gr Failsafe. The same powder charge will normally give a little over 3000fps in other rifles and with the Failsafes likely would be a little too warm.
When I get too it, I'll measure the throats on the Kimbers and Sako's for further comparisons......................DJ

Interesting. Never really gave it much thought, one barrel being faster than another seemingly identical one. I would say bore diameter would be a factor along with the bore finish, a polished/lapped bore being faster than a rougher bore which would result in more friction/drag on the bullet. As far as throating being a factor, I have no clue.

I have 2 7X57 rifles with identical 19" barrels. With the same ammunition one shots about 100fps. faster than the other. They are both long throated with one being longer that the other. As I sit here I know not which is the longer throat. roger

Just to muddy the water a little more:
Last year, I switched .308 barrels on my M-7, going from the 18 1/2" to a .22" tube. I figured I'd gain in the neighborhood of 100fps. Guesses usually run about 25-30 fps per inch, right?
Well I gained velocity alright. A whopping 50fps! This from the same batch of loads. Some things never cease to amaze.

Chronographs are a bitch! I see this often in handguns & rifles. It's one reason to own or have access to a chronograph. There are many shooters out there shooting their 7remmags @ .280 vel.

Chamber size, throat length, bore diameter, bore smoothness, depth of rifling and maybe a few other things, all effect velocity. Very rare to have any two guns shoot the same even from the same maker.
Sometimes the slower gun can use a little more powder safely because the pressure is "usually" lower. Just be sure to work carefully.

i would bet that two barrels off of the same mandrel (one after another) chambered by the same gunsmith would still give variation such as these! one of our gunsmith members might comment.
james

I built two 340 wildcats. Both exact same Douglas barrel. Same MKX actions Cut with the same reamer the same day. Headspaced as close as I could make them. Same bullets, same powder, same primer same day at the range over the same chrono and they are 75+/- apart. Different bullet shape and powder and the slow rifle is 30+/- faster.

quote:

Originally posted by J Stambough:
i would bet that two barrels off of the same mandrel (one after another) chambered by the same gunsmith would still give variation such as these! one of our gunsmith members might comment.
james

I know they would. No two bbl. blanks can be the identical. Internal stresses from manuf. pretty much guarantee variation.

I actually have 2 Kimber 270 WSM's. Both of them Chronographed within tolerances of each other with the same load. The Sako also shot a 130gr TSX load about the same amount slower than the 2 Kimbers did.
I think that such large variation would be quite unusual to find in 2 otherwise identical guns from the same maker. But then again it's pretty unusual to have 2 nearly identical rifles from the same make to test this theory also.
It just seemed more signifigant to me because my other Sako WSM (a 300 WSM) shot signifigantly slower than other 300 WSM's I'd shot of the same barrel length. I really think it's something to do with the long throating and perhaps a slightly larger bore.
I read somewhere (can't remember exactly where) that there tends to be lots of bore variations in 7mm rifles. Perhaps that's one of the factors in why 7mm Rem Mags tend to vary a good bit in velocities - the one's I've had did. But remembering reading something and having more definate proof are 2 different things!........................DJ

26" barrel w/slop hole chamber and oversize throat = 2725fps
25" barrel w/tight chamber and minimum throat = 2995fps

Same receiver, same lot of ammo, same barrel. I had 1" removed from the breach end and than re-chambered to eliminate the piss poor gunsmithing.

quote:

Originally posted by djpaintles:
I actually have 2 Kimber 270 WSM's. Both of them Chronographed within tolerances of each other with the same load. The Sako also shot a 130gr TSX load about the same amount slower than the 2 Kimbers did.
I think that such large variation would be quite unusual to find in 2 otherwise identical guns from the same maker. But then again it's pretty unusual to have 2 nearly identical rifles from the same make to test this theory also.
It just seemed more signifigant to me because my other Sako WSM (a 300 WSM) shot signifigantly slower than other 300 WSM's I'd shot of the same barrel length. I really think it's something to do with the long throating and perhaps a slightly larger bore.
I read somewhere (can't remember exactly where) that there tends to be lots of bore variations in 7mm rifles. Perhaps that's one of the factors in why 7mm Rem Mags tend to vary a good bit in velocities - the one's I've had did. But remembering reading something and having more definate proof are 2 different things!........................DJ

dj, you just got lucky my friend. I've seen the opp. more than your example.

One of my favorite anecdotes is of an ammo manufacturer who bought ten "identical" test barrels to SAAMI specs from the same maker, same steel, same reamer, ... samo. Nine barrels fired reference ammo to spec. The tenth would not. In spite of lapping, break-in, etc. it would not match. The measurement lab could not distinguish the "bad" from the "good". They paid the barrel maker, and scrapped the barrel.

Yes, there are significant differences in even "identical" barrels. Just because we can't pinpoint the differences doesn't mean that they aren't there.

KenO

Over 30 years ago using a model 33, A friend and I had access to 3 different model 29's; a 4", a 6 1/2" and my 8 3/8". The velocities with the same box of factory Remington 240 grain JSP's favored the 4", the 6 1/2" and lastly the 8 3/8". Thank God mine is the most accurate of the 3!

What this means is that there is far more to the velocity quandry than just barrel length or throating, and as Dr Ken points out even the unmeasurable.

I have experienced this with quite a few rifles.

Internal dimensions make all the difference in the world.

I see this a good bit in 7RM, 270 Win, and 25-06. It happens in all others as well but, I seem to notice the largest difference in the referenced carts.

Out of the 3 7RMs I own the shortest bbl is the fastest

Until you run them over a chrono, barrel length means nothing! The longer barrel is only faster if you are comparing the SAME barrel(IE if you cut some off it will shoot slower in that given barrel)

Good Luck

Reloader

I have seen cases of barrels being faster than other but never ones being slower.

quote:

Originally posted by KSTEPHENS:
I have seen cases of barrels being faster than other but never ones being slower.

Can't have one without the other can you?.....................DJ

quote:

Originally posted by djpaintles:
...Do you think the difference in Throating could cause this much velocity difference? Do Sako's maybe have a little bit larger bore diameter? ...

Hey DJ, Perhaps it is a combination of both.

Many years ago I had a lot of the original Ruger M77 rifles(Tang Safety era). I've heard they out-sourced their barrels back then, but the ones I had, all had larger Bore Dimensions.

You could take a Bore Brush which would "feel" loose in those M77s, use it in a M70 or M700 and it would be a snug fit. For certain calibers, it was actually best to use the next size larger Brush with those M77s. It is easy enough to "feel" if you have a Bore Brush that has been used a good bit with JB Compound.

Rifles like that are a mixed blessing. You can "normally" use a bit more Powder - Safely - and get some high velocities. They can also easily mislead a Beginner, which would not be a concern for you.

Probably gonna need seperate ammo for the Sako to utilize the plus side. The M77s were kind of "picky" about which Powder and Bullets they needed in order to shoot small groups, as well as I can remember, but they would eventually shoot fairly well.

Best of luck to you.

On my Sako 300 WSM I ended up using a max listed load of Mag-pro and ended up at about 2925fps or so with 180gr Fail-Safes. I think in a normal 300 WSM the same load would have been too warm and over 3000fps. It shoots extremely well and the Fail-Safes are awesome game bullets.
I've loaded up some stiff loads with RL-22 and MagPro in graduated increments and will head to the range with a Micrometer to mic head expansion to help double check that I'm not getting too warm. We'll see what happens. Hopefully I can make it to the range tommorrow.
The Sako 85 shoots accurately but I can't get too exited about a 270 WSM that shoots the same bullets to the same speed as my Mato 270 Winchester............................DJ

It is for things like this that I do some of the "odd" things while reloading.

I have two .223's, and use Win cases on one and Rem cases on the other. Both shoot just a bit different, and while I don't load hot, I don't want to take any chances.

A few range buddies think I am bit anal to do that.

I would think that variation is perfectly normal ,150f/s between 2 rifles averages out to 75f/s differance. By the time the slower one becomes broken in or self lapped by shooting the differance will be negligable.

quote:

Originally posted by J Stambough:
i would bet that two barrels off of the same mandrel (one after another) chambered by the same gunsmith would still give variation such as these! one of our gunsmith members might comment.
james

James, you have hit it right on the head!

It could very well be the throating that is responsible for this. But I have seen "IDENTICAL" barrels, made on the same machinery from the same steel and chambered with one reamer, ONE RIGHT AFTER THE OTHER, that shot this way-one faster/more accurate than the other. And there was no obvious or detectable reason for the performance difference.....