Recently bought an ANNB one of the FN/Winchester Model 70s in 270 WCF. In keeping with the silly trend toward shorter barrels, it is equipped with a 22" barrel rather than a 26", as it should.
(It a'int no brush gun).
When loading data is looked over it all seems to be for 24 or 26" barrels and 4350/4831 give the best results with 130/150 bullets. They don't give the best results in the 22" and I have been playing with 4064, 3031 and 4320.
Wonder if anyone can save me a lot of experimenting based on their experience.
So far my best accuracy (1 MOA) has been with Combined Technolgy and Nosler Accubonds, both 130s.
The FN/Winchester is a beautiful rifle, far better in fit, finish and smoothness than my 2008 New Haven CRF 270.
Thanks in advance.

I've got a very old (1968 vintage) BDL in 270 with a 22" barrel. I shoot 150g Partitions at 3000 fps with sub MOA accuracy. It also shoots Sierra 90g HPBT (varmint rounds) at 3500 fps in .5" groups at 100 yards.

My load and work up with caution is: Rem brass, Federal 215 (magnum!) primers, 58.5g H4831, 150g Nosler Partition bullets seated 1/10" short of the lands. I neck size only, so my cases are a tad bigger. I fire form using my Sierra 90g HPBT loads.

I recently gave my 270 to my youngest son (who is right handed like me). My oldest son got the matching left handed rifle I bought for my father in-law 20 years ago. Here's my youngest with his first elk and his first feral hog. Note the Rem 700 BDL in 270 in both pictures.

i bet you loose less than 100fps with your 22inch tube. I have a pre 64 with a 24 and jc higgind with a 22, difference is irelivent.
I have a 20 in .257 roberts that shoots faster with the same loads than my 24 inch roberts...tj3006

Well the 4831 didn't work for me (through a chronograph, not trusting book data).

As for 22 vs 26, the difference is a lot more than 100 fps especially with the slow burners.

Won a lot of chronograph bets with my 26" 300 H&H 721 shooting against 22" 300 WSMs.

I just tried some Superperformance in my 25-06 which pushes out an 80 gr TTSX at 4000 (28" barrel). Worth a try in the 270 as it is so much denser than any of the stick powders more will fit in.



Shot 3 in 1.5" @ 200 this AM with only a 3-9 Conquest.

quote:

Originally posted by 45-70 shooter:
Recently bought an ANNB one of the FN/Winchester Model 70s in 270 WCF. In keeping with the silly trend toward shorter barrels, it is equipped with a 22" barrel rather than a 26", as it should.
(It a'int no brush gun).

This isn't a silly trend.....Winchester has been producing a .270 with a 22" barrel since the pre-64 days and Remington actually made a M-700 in .270 with a 20" barrrel
When loading data is looked over it all seems to be for 24 or 26" barrels and 4350/4831 give the best results with 130/150 bullets. They don't give the best results in the 22" and I have been playing with 4064, 3031 and 4320.
Wonder if anyone can save me a lot of experimenting based on their experience.
So far my best accuracy (1 MOA) has been with Combined Technolgy and Nosler Accubonds, both 130s.
The FN/Winchester is a beautiful rifle, far better in fit, finish and smoothness than my 2008 New Haven CRF 270.
Thanks in advance.

Best performance (FPS) in a shorter barrel is the same load as gave the best performance in the longer barrel.....accuracy however is a crapshoot....one simply has to experiment.

Try magnum rifle primers (Federal 215s) really. They do make a difference. If your load is at max already back off 2 grains and work your way back up.

I think you're moving in the right direction when going to the slightly faster burning powders. Although 3031 and or 4895 will do the job, I'd be looking at A-XMR-4064. H380, h414 or Accurate 2700.
A little side note: As a much younger fella I had a hunting partner that used a 30-06 mod. 760 with an 18" barrel. When it came to Mule Deer and Elk he was the top meat getting hunter in our area. I just guess he didn't know he should be worried about velocity loose 22" barrel??? See no problem there. roger

The load that gives you the best speed in a long tube with also do so in tha short tube. I have proven this over my Chrono with barrels from 15"(Encore Pistol 308win/257Roberts/25-06/30-06) to 18"(308win) and 20"(30-06) and 22-24" barrels. Same goes with pistol rounds in short vrs long. There will be more muzzle flash in shorter barrels.

I also have used Win 760 in 30-06 rifles(and pistol) with 18 and 20" barrels and have killed many, many deer etc with them while my friends were using long barreled mags and not doing as well.

Use whatever powder gives the best accuracy and try the loads which show the most speed first for hunting.

22" is pretty much the standard barrel length for the 270 WCF. I've been loading 270 for almost 30 years now for about a half dozen different rifles and have chronograph data for most of them. All but one of them (a pre '64 M-70) are 22" barrels. Using 60.0 H4831 and Hornady 130s all but one of them run 3120 to 3150 fps. A Remington M-700 had an oversize chamber and gave about 120 fps slower velocity with that load. In three different rifles I have similar results using 58.0 IMR4831. The pre '64 M-70 has a 24" barrel and gives about the same velocities as the various 22" guns. With 150 grain bullets in various rifles I have gotten 3000+ fps using IMR4831, RL22 and Accurate 3100. With either bullet weight I have never found the need to go to faster powders for top performance in a 22" barrel. Based on my experiences I believe that differences from barrel to barrel cause as much velocity variance as + or - 2" of barrel length.

Sagebrush, my experience equates with yours. Though now I have a recently acquired 1950s vintage Weatherby Mark V in 270 Weatherby with a 26" barrel. Going to start working up some loads with 150g Partitions. Hoping to get 3300 fps.

quote:

In keeping with the silly trend toward shorter barrels, it is equipped with a 22" barrel rather than a 26"...

What an odd and inaccurate statement. Jack O'Connor (know who he was?) owned a handful of .270s during his lifetime. His favorite .270 had a 22" barrel and was built for him in 1953. He owned several with 24" barrels but he thought they were too long and heavy for a mountain rifle. His were certainly not brush rifles but were used on sheep, antelope, mule deer, etc.

Use whatever barrel length you want of course, but the premier authority on the .270 thought that 22" was just fine. BTW he used H4831 for most of his 130 and 150-grain loads.



.

IMHO the "trend" toward shorter barrels is just more BS foisted on us by gun writers. One says it and the rest repeat it with no testing or evidence. Has anyone a verified, documented story of any hunter being killed because his rifle barrel was too long ? Good old Mauser actually built hunting rifles in the interwar years with 28" barrels .... they appeared to work just fine.
My M 70 would be a far better rifle from a ballistic and balance point of view if it had a 26" barrel, just as my 1952 721 300 H&H is a far better rifle than a 300 WSM with a 22" barrel.
My 1930s RF Sedgley Springfield deluxe sporter in 6.5x55 has a 27" barrel. It is more accurate than the 264 win mag (although not as fast) and among other common 6.5s is only beaten by the Savage F class 6.5x284. We've made little real progess in ballistics.

The 6.5 is the top one. ((any factory model 70 could only wish to equal this rifle built on a DHT NM action))



Have loaded up a bunch of different .277 bullets (130,140,150) with max loads of 4350. They were all accurate in my 721 (24") and Marlin (22") well see how they do in the 70 and thru the Chrongraph.

Those are a pair of beautiful rifles. I am seriously considering being consumed with jealous envy. Sounds like they shoot as good as they look. On the subject of barrel length, shoot and carry what you like - just expect the rest of us to do the same.

I can't recall having ever seen a factory built bolt rifle in .270 with a 26 in barrel.
I uave seen ruger #1s.
no game animal would show a difference beetween a 22 and a 24 inch.
the difference in velocity would be completly irellevent.
and the powder that works well at 24 would work well a 22 also.
...tj3006

2 or 4" of barrel length will not make up for the fact that most of us could afford to lose 10 pounds, spend more time at the gym and trim what else we carry. JOC was an excellent writer, but not always right. I have no doubt I could build a Cooper or Kimber "mountain rifle" (how many of the members here really have ever hunted in "the mountains"?) with a 26" barrel that would weigh less than any of JOC's Model 70s. I do hunt "in the mountains" as my house sits at 7200' which, in most of USA is already a "mountain". The objective of any barrel is to maximize the powder burn and accuracy. Ever seen a handgun hunter using a 2" barrel ? Long barrels shoot faster, are more steady and the "weight issue" is just BS. Another fad foisted on the gulliable by gun writers and marketing types, just like huge scopes with countless knobs to get turned while the Elk walks into the timber.
The FN model 70 is a handsome rifle and may, with more load work, become a 3000 fps sub MOA rifle.
BTW, if you own an older edition of Pet Loads, look at the "JOC box" in the 270 WRA section.
The loads he quotes (absent pressure transducers and chronographs) are at or beyond today's accepted maximums.
I had (and foolishly sold) a classic 270 WCF 03 actioned replica with a 27" full octagon Badger barrel. 3200 fps with 130s was no problem and it shot bugs off the target.
It weighed 9.5 pounds all up which was less than I saved by switching my pack, tent, sleeping bag, stove, boots etc. to today's state of the art products comapred to my former 1960s stuff.
Finally, I'm still waiting for the list of all the hunters killed because the had "long" barrels.

Just got back from shooting my 1950s vintage 270 Weatherby that I recently picked up for under $1000. Three 5 shot groups all better than .75", one better than .5" at 100 yards shooting some cheap Weatherby factory 130g loads (cheap for Weatherby) at 3250 fps. It has a 26" barrel, just because it does. My 1960s vintage BDL in 270 gets over 3000 fps with 150g Partitions and still shoots 3/4" groups after several thousand (4?) rounds through the original barrel. I just bought the Weatherby because I gave my BDL to my youngest and always wanted one. Now to decide whether to take the 270 Bee or 500 Jeff elk hunting lol ...

270 Bee

quote:

Originally posted by 45-70 shooter:
2 or 4" of barrel length will not make up for the fact that most of us could afford to lose 10 pounds, spend more time at the gym and trim what else we carry. JOC was an excellent writer, but not always right. I have no doubt I could build a Cooper or Kimber "mountain rifle" (how many of the members here really have ever hunted in "the mountains"?) with a 26" barrel that would weigh less than any of JOC's Model 70s. I do hunt "in the mountains" as my house sits at 7200' which, in most of USA is already a "mountain". The objective of any barrel is to maximize the powder burn and accuracy. Ever seen a handgun hunter using a 2" barrel ? Long barrels shoot faster, are more steady and the "weight issue" is just BS. Another fad foisted on the gulliable by gun writers and marketing types, just like huge scopes with countless knobs to get turned while the Elk walks into the timber.
The FN model 70 is a handsome rifle and may, with more load work, become a 3000 fps sub MOA rifle.
BTW, if you own an older edition of Pet Loads, look at the "JOC box" in the 270 WRA section.
The loads he quotes (absent pressure transducers and chronographs) are at or beyond today's accepted maximums.
I had (and foolishly sold) a classic 270 WCF 03 actioned replica with a 27" full octagon Badger barrel. 3200 fps with 130s was no problem and it shot bugs off the target.
It weighed 9.5 pounds all up which was less than I saved by switching my pack, tent, sleeping bag, stove, boots etc. to today's state of the art products comapred to my former 1960s stuff.
Finally, I'm still waiting for the list of all the hunters killed because the had "long" barrels.

I also live and hunt in the mountains. My home is at 6200', most of my hunting is a t 6500' to 8000' and I took my bighorn sheep at 12500'. Yes, I should lose some weight and get in better shape, but I still appreciate a lighter (8 lbs or so) rifle when tramping up and down or through the brush. On level open ground a heavier rifle is OK.

On length, I don't know of any hunters who were trampled by buffalo or hippo because their 26" barrel got caught on something. Murphy says that it will happen. I do know some hunters who swung their 22" 458's into buffalo busting out of a bush, dropping the brutes. But do I listen to myself? My 416s are 25" though my 500 AccR is 22" and I've even contemplated 20". We all learn to adapt to the tools that we have. I suspect that those who jammed a 22" barrel into a buffalo hide, squeeze-bang, would have done the same with a 25".

On loads, you might want to check out some of the new powders like Rel 17, something great in my wife's 270, or that Hodgdon superformance stuff (which I haven't tried). Her 22.4" barreled rifle (yes, it's a Tikka) shoots the 110 TTSX at 3400-3450. Sweet.

45-70 shooter

I just read an article in Handloader magazine, No 279, about barrel length, written by Terry Wieland. He had 2 rifles, #1a p-17 enfield in 30-06 26" barrel #2 1896 Swedish Mauser 6.5X55 28" barrel.He used one factory load and three handloads with three different bullet weights in both rifles. Terry then preceded to cut off 2 inches of barrel on each and then re-test for velocity.

to quote Terry "It would seem that optimum barrel length in a 30-06 is 24 inches, but reducing it to 23 or even 22 would not cause great loss if you are careful how you handload.In the 6.5X55, optimum length is 22 inches, but even 18 inches can deliver good results with the right load" He goes on to say "In all five loads tested with the 6.5X55, there was startling velocity loss between 18 and 16 inches.The load that lost the least was a combination of a 140gr Sierra GameKing and IMR-3031. From 28 inches to 18, it lost only 105 fps (dropping from 2,464 to 2,359) but then plunged and additional 81 fps after the cut to 16 inches.

Now sir you talk about mis-conceptions from gun writers, but some actually do real world test. Your statement that longer barrels burn powder better is just not true. Most if not all powder is burned with a couple of inches from the chamber. A 2 inch pistol barrel is comparing apples to moon rocks and is mis-leading.

Terry's final conclusion, from ACTUAL test with two different rifles firing 5 loads each was that the 30-06 lost 27.2 fps per inch of barrel length and the 6.5X55 lost an average of 26.57 fps per barrel inch. This is very close to the often stated 25 fps velocity per inch of barrel.

So if your 100fps gain with a 26 inch barrel, over 22" will make you sleep better at night then have at it, but to put down, or claim that people are gullible, is kind of condiscending, kind of, but the facts remain, and 22 inch barrels are not "short" for non-magnum cartridges. Like most have said here, if you like it then great, but facts are facts......

quote:

I had (and foolishly sold) a classic 270 WCF 03 actioned replica with a 27" full octagon Badger barrel. 3200 fps with 130s was no problem and it shot bugs off the target.
It weighed 9.5 pounds all up which was less than I saved by switching my pack, tent, sleeping bag, stove, boots etc. to today's state of the art products comapred to my former 1960s stuff.

And my box stock BDL with a 22" barrel shoots handloaded Speer GS 130s @ a consistent 3150 fps into cute little "Mickey Mouse ears". Please tell me what your extra five inches of barrel and extra pound and a half gain you, other than a knot in your shoulder from a full day of packing and a collar full of snow time and time again because the barrel is so long.

Yes, I have been to the mountains... several times.

As stated above, facts are facts. Shoot what you want, but don't try to convince all of us to shoot your 28" barrels. Most of us don't need to (or want to, for that matter).

So you are telling me ONE/TWO pounds will make or break a complete hunt ? OK, if you say so.

Killed a Bighorn at 12,500". Who carried the "Oh two" tanks ?

Shot the 270 today (and 300 H&H) and will be posting results later. Right now just looking for a load that is as accurate as my el cheapo Marlin 270 (not there yet) with the same powder and bullets. Not that 1 MOA is bad but ......

270 results today. Cool, no wind, no mirage, 7000', 65 degrees.

All these loads and bullets will shoot sub MOA in both my old 721B and Marlin XL7C rifles. The former wearing an old 6X Redfield (26mm!) and the latter a Nikon Coyote Special. The XL will drop 5 135 SMKs in one ragged hole !

Took the 70 apart, no bedding issues, barrel full free floated (as are the other 2), scope is a Trijicon 3-9 in Talleys. IME 4350 ALWAYS works in a 270. The 130/5s used CC 250s the 140/50 regular WW LR.

The barrel was cleaned with wipe out, then sweets,then JBed, then Hoppe's (each was neutralized after each step with acetone). That barrel was a clean as shiny in the borescope as Obama's honesty.

The results were somewhat acceptable. In 55 years of handloading a LOT of 270s have come and gone. This one is a challenge to say the least.

Next step, drop back to 1 gr above "starting loads" with all suitable powders on my shelf and the 135 SMKs and try several loads with the TTSX (my hunting bullet of choice).

More to follow:

[QUOTE]Originally posted by 45-70 shooter

Killed a Bighorn at 12,500". Who carried the "Oh two" tanks ?

That was quite a hunt. Only time I've ever hired an outfitter/guide and I'm glad I did. The hunt was in the Maroon Bells wilderness area just outside of Aspen, CO. We rode horseback in to our base camp at the headwaters of East Maroon Creek at a bit above 11,000'. The hunting was all on foot at elevations ranging from 11,000' to 12,500'. The guide worked my @$$ off but took good care me and I got my ram on the seventh day of the hunt. The real fun was getting the meat and trophy back down to the trail... I was packing a Winchester M-70 Featherweight and was sure glad it wasn't any heavier than it was. Load was a Hornady 140 BT over RL-22 at 3100 fps. A one shot kill at 235 yards (the guide had a range finder) and a very happy hunter and guide.

I do not understand the issue with 22" barrels, if you don't like them, it's pretty simple to not buy them.

I have owned a plethora of 270's with barrels from 18-28" and bullet weights from 85-160gr.

My starting/goto load anymore is 60gr of H4831sc, over 130gr bullets and a WLRM primer.

The bullets I use are Hornady Interlock and GMX, Nosler BT's, Barnes TSX & TTSX.

Velocities vary from 3050 to 3150 in my various rifles with 22"-24" barrels.

I do not like barrels shorter than 22" due to muzzle blast. On the other hand I do not like barrels over 24" as they don't seem to handle and carry as well for me. Just my preference, your mileage may vary of course.

For 45-70 and the nice featherweight:
It's always interesting trying to figure out a rifle. Let's assume that there is no scope movement nor that the bedding shifts. It seems that the classic 55gn (54.5gn) IMR 4350 with 130 grain is on a scatter node for your gun. Strange.
I would also try 56 grain if you don't have pressure signs. And especially try R17. It has a different rate burning curve which might move the scatter node and give you something sterling at 55-56 grain with 130gr.

Reading the original post, if you haven't tried either of the 4831s yet, you owe it to yourself to do so. In my experience they are "can't go wrong" choices in the 270 WCF.

Thanks for the thought, but 4831 is even slower (less velocity, more muzzle blast)
Looked back in my "270 file" and found several cases of fine accuracy with Varget and std WW primers. Loaded up a bunch with different bullets to try out. Not hyper fast but 2950 will kill anything I'd hunt with a 130 in a 270 WCF.

Here's a group shot with my youngest son's BDL in 270, 59g H4831 pushing a 150g Partition at 3030 fps out of a 22" barrel. This is a larger than normal group out of this rifle but still under 1" center to center at 100 yards, I blame myself for the flyer on top. Usually all three will cut the same hole.




Here's a better group shot the same day, same load.

quote:

Thanks for the thought, but 4831 is even slower (less velocity, more muzzle blast

FWIW, that 3150 load I posted about earlier is 60 grains of AA 3100 lit by a CCI-200, and a projectile seated .010" off the lands... If you know anything at all about Accurate Arms powders you know the now discontinued 3100 is cotton based 4831. As was explained to me by their ballistician quite a few years ago, "our powder is identical to IMR 4831, but is one grain slower because it is nitrocotton based as opposed to nitrocellulose based".

So much for "slower and more muzzle blast"... the more you post the more I am disinclined to believe you know what you are talking about.

May I suggest you download a current powder burn rate chart and read it.

http://www.hodgdon.com/burn-rate.html


4831 is a slower burning powder than 4350 .... end of story.
FYI, most loading books suggest using Magnum primers with 4831 and you don't seat Barnes bullets .010 off the lands.

To suggest that a slower burning powder does not generate lower velocity and more muzzle blast in a short barrel makes me disinclined to believe you own a Chronograph and have ever shot the same loads in a 22" and 26" barrel.

Simple example. Load up a max load of 2400 in a 44 magnum with a 240 gr bullet. Shoot that load in a 3" and 8 & 3/8" S&W. First through a Chronograph and then in the twilight. Betcha a steak dinner the longer barrel is faster and produces far less flash/noise. Now explain to me why things are going to be different in a rifle.
In the 270 WCF, 48 gr of Varget gives the same velocity as 60 gr of H4831. (that in a 24" test barrel). That would suggest to me the Varget is considerably more efficient and will be even more so in a shorter barrel.

Heading to the range tomorrow to see if the Varget load groups and with what bullet. Then I'll worry about chronographed velocity.

I was guessing your experience was with handguns and shorter barrels. The difference between an 8" barrel and a 3 3/8 inch barrel is over 200%. The difference between a 26" barrel and a 22" barrel is less than 20%. So expect to see 1/10 of the difference you see from your handgun loads. Find what works best for you, good luck!

In my Ruger Ultralite 270 with a 20" barrel, I am getting very good accuracy using 140 gr Accubond, 52 grs 7828SC, and CCI 250 primers.

quote:

The difference between a 26" barrel and a 22" barrel is less than 20%.

a LOT less

Today's results with Varget.
As I had mentioned my "270 file" showed good results years ago with Varget. Filled up the old Lyman measure and got it dropping 44.5 +-1/10.

Pretty clear what it liked and did not. The 150 Combined Tech (now ballistic silvertip) load was, on paper, a bit warm for a generic 150, but being a coated bullet exhibited no pressure signs. Clear, no wind, 7000', 1" of mirage @ 100, shot in groups of 3/4, 5 minutes between groups, one minute between shots.

I don't hunt big game with regular ballistic tips as several have not made "two holes" in Deer or Antleope. The CTs/BSTs do.

So I have a fine bullet and powder. next step, fire up the RCBS electronic measure and load up a bunch in 1/2 gr increments, running them through the Chronograph. Hodgdon/Nosler data appears conservative as many report 3000 fps with various 150s. As we all know every barrel is different so moving up slowly is prudent.

An interesting aside is that the rifle is not an FN/Winchester as I found out when I pulled it from the stock to check the bedding. Although the fit and finish are far better than other late new Haven guns, this one is so marked and has the "real" model 70 trigger (thanks be to God!)
The former owner, as well as spending a fortune on the Talleys and threaded stud turn in swivels, also bedded the action in "The Whelen Method" which, IMHO, is the only way to bed a sporting bolt action rifle.

Todays results: 1/2" on centers from a lightweight rifle with a picket post reticle in a Trijicon 3-9 is quite pleasing. (last group)

quote:

Originally posted by Doubless:
[QUOTE] If you know anything at all about Accurate Arms powders you know the now discontinued 3100 is cotton based 4831. As was explained to me by their ballistician quite a few years ago, "our powder is identical to IMR 4831, but is one grain slower because it is nitrocotton based as opposed to nitrocellulose based".

So much for "slower and more muzzle blast"... the more you post the more I am disinclined to believe you know what you are talking about.

Since when is gun cotton different than nitro cellulose? roger

quote:

Originally posted by vapodog:

quote:

The difference between a 26" barrel and a 22" barrel is less than 20%.

a LOT less

Agreed, in velocity more like 3% difference or 30fps per inch at over 3000 fps. I was just talking about relative barrel length percentage change.

Lyman, who I suppose know less than "our" experts says:

"For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24 inches down to 20 inches with the following results:

The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch."

Four times 37 is 148. Add the muzzle blast, less steady hold and you have something worth comment.
Especially in a cartridge not intended for short range jump shooting in the dark woods.

You keep believing your 4350/4831 130 gr loads are yielding 3000+ fps in 22" barrels. I'm having trouble finding any bullet or powder maker who agrees. All my load books show 24" or longer barrels.

In any case, my post was not intended to start a "mine is bigger" fight with no ruler supplied.

I'll press on with Varget and the 150 BSTs as MY rifle seems to like that combo. My current load should be at about 2600 fps (sea level). We'll see what adding a bit more Varget plus being at 7000' feet can do.

BTW, Chuck, Nosler only rates any of their 150 gr bullets at 2782 fps with a 24" barrel with 52 gr of 4350 the SLOWEST powder listed. So you are adding 7 grains of an even slower powder (over published max from Hodgdon), lopping 2" off the barrel and picking up almost 300 fps while shooting bugholes with Nosler's least accurate bullet. Hodgdon lists the MAX H4831 load as 55.7 gr @ 2804 fps with a 24" barrel (corrected for sea level and velocity at the muzzle).
I'd be treasuring that 700 !

quote:

I'll press on with Varget and the 150 BSTs as MY rifle seems to like that combo. My current load should be at about 2600 fps (sea level). We'll see what adding a bit more Varget plus being at 7000' feet can do.

elevation will affect the Ballistic coefficient calculations and travel to the chronograph, not the muzzle velocity per se.

If you want to calculate back to a MV from a chronograph see JBMballistics.com. The trajectory generator (free) has inputs for (Measured) Velocity as well as distance of chronograph from the muzzle and BC and altitude, temp, and humidity, so that everything can be neatly accounted for. For some reason I like to set my chronographs at 20 feet, seven paces minus a foot. Broad approximations on temp and humidity are OK, they rarely affect more than an inch out at 300-400 yards. The BC of the bullet is the big factor, including measuring of the muzzle velocity, resulting in variations of +8 to +30 fps, depending on BC. Bullets in the .100-.200 BC range may actually have a muzzle velocity 30fps faster than the 20 ft. chrono lists. typical hunting bullets with a .4 BC may have a +10-+15fps gain.

My Nosler manual #6 list powders as fast as IMR4320 to as slow as Mag pro and IMR7828 with 150 gr. bullets. The fastest load shown is MagPro at 2913 fps.