Home Forums Hunting & Shooting Hunting Rifles Fast vs slow barrels and such.

I know this has been kicked around some but I still have inter-related questions for the more experienced.

Are "fast" barrels supposedly due to slightly smaller bore diameter, resulting in more pressure for any specific load, hence more velocity? Or are there other reasons?

If the above is reasonable, might the slightly larger bore diameter "slow" barrel be loaded with slightly more powder, and still be at safe pressure?

Lastly, in any rifle slow or fast, can greater capacity brass be loaded with slightly more powder and still be at safe pressure?

What do you mean by "fast" or "slow".

Twist? In relation to length? Or just 2 barrels of the same chambering, length, and twist shooting different velocities, given same bullet and powder charges?

I see reports here that some rifles are able to get more velocity than other rifles of the same chambering.

For instance, in 7mm-08 with 140 grain bullets; some can safely get 2900fps, while others can only get to say 2750fps safely, without obvious pressure signs.

I think you'll find that except in extreme cases, rifles are going to clock +/- 50 fps over what one would expect in a given chambering for a given barrel length.

As far as a gun that is 200 fps faster than expected, yes you can get high velocities if you load hot. Obvious pressure signs show up at somewhere in the 72-73,000 psi range. Some people are content loading that hot, others are not. There is no free lunch with velocity, the only way to get a small case to achieve larger case velocities is to run high pressure loads.

I once had a 35 whelen ackley and I was pushing 250 gr bullets 2700 fps. It wasn't some magically fast barrel, I was just loading it to just under primers falling out of the case pressures. The only reason I loaded it so hot is that it wouldn't group if I backed off the loads. But I just wasn't comfortable running a rifle so hot, so I had it re-chambered to a 350 rigby. With the larger case I could get 2700 fps at reasonable pressures, and more importantly the real gunsmith I used to do the work trued up the action and barrel and it shot much better, and would still group when backing off the loads.

Between friends and family over the years I've loaded for 7 different 30-06's. One had a 24" barrel, one a 20" barrel, the rest 22" With the same loads one of the 22" guns was consistently the fastest, beating out the 24" gun by a small margin. One 22" gun was consistently the slowest, even slower than the 20" rifle. There was about 130 fps difference from fastest to slowest. If I exclude the 20" rifle, and the "slower" 22" gun all the rest are within 20-30 fps of each other.

I don't know exactly why, but those were my observations.

Some rifles have headspace tolerances that can cause pressure issues at much lower velocities. A badly fouled barrel may also cause an issue.

For the most part if there is not a mechanical issue I don't think you will see much more than 50 fps either way.

If there's a 150 fps difference in barrels of equal length I'd be looking for the underlying cause.

Shod

I have four rifles chambered in 6.5-284, three with 24" barrels and one with a 22" barrel. The 22" barrel shoots the same loads faster than all three 24" rifles. Are the three 24" slow or is the 22" barrel fast? I don't know the answer, but know that the 22" barrel is always faster with every bullet/powder/primer combination that I've tried from 95 grain VMax to 140 grain Partitions. Even though the 22" barrel rifle is a long action Winchester 70 and the 24" barrel rifles are build on short actions, Remington 700, 722, and Savage 99, the COAL is kept the same.

I read a recent post by a very reputable and accomplished shooter on another site who was mounting scopes and setting up 16 identical factory new rifles in 416 Rigby. He had been provided a case of factory ammo to get them all dialed in. He was curious about it so chrono'd them and found a difference of over 150fps between the fastest and the slowest. Quite amazing experiment with 12 new rifles shooting the same lot of factory ammo in a controlled environment.

It;s common to see some barrels chambered for the same cartridge give more velocity than others and it can be interesting to dwell on why. I did for years and built a lot of barrels with different internal dimensions,twists, throat lengths, etc; worked with cut rifled, button rifled,and hammer forged barrels in an attempt to find out "why".

Within pretty broad parameters some very general patterns emerged but there were always enough exceptions to keep a guy still guessing about it all.

Through all this, one universal "truth" emerged,and especially when it came to getting the velocity desired with heavy for caliber bullets(whatever that velocity might have been)...and that was.....get a bigger cartridge.

This worked every time it was tried regardless of the barrel. The "variations" in velocity between barrels still showed up but it didn't matter if you have a big enough engine to do the job in the first place.

And the other thing was that lighter for caliber bullets lied a lot,frequently coming so close in velocity from a smaller case to a larger one that it led to false conclusions (like "my 7/08 is as fast as a 280 with the same bullets".... It isn't. That's pressure).

So my bottom line is that, if I want(say) a 140 gr 7mm bullet to do 3000-3050 fps from a 7mm caliber cartridge, buy a 280 Remington and don't pound on a 7/08 to get it.Then forget all about the "fast barrel/slow barrel" conundrum.

Like I said, it works every time.

Yes

I put together two 257 Ackleys several years ago with master metalsmith Ron Lampert doing all the work. One was built on a pre-64 M70, the other on one of the first SA push feed M70's. Other than that difference, the two were exactly the same as far as barrel manufacture, barrel contour,barrel length and reamer used. However, with cartridges loaded the same, one would always push a bullet through the chrono 100+ feet per second faster than the other. Group size was the same.

BobinNH,

Your post was filled with excellent information, which I don't doubt. But I don't think it really addressed the question. I don't think the OP was trying to turn a 7-08 into a 7 mag, just trying to understand WHY there was such a difference in speeds with the same ammo. At least that is my question.

I've experienced more than 100 FPS with ammo from the same box in guns of equal barrel length several times. A difference of 25-50 fps seems common. But based on my observations the fastest speeds are the ones that are pretty close to where they should be. It is the guns that shoot 50-150 fps slower than what the factory specs or loading manuals say they should be that are the question.

I've always heard, and believed it is due to looser tolerances in the chambers and barrels creating less pressure. Truth, or myth?

Three different barrels, different brands, 24 and 25", all 14" twist, all chambered with the same 223AI reamer by the same person. Same exact load, there's 150 and 200fps difference between two slower barrels and the good one.

My Freedom Arms .454 has a 10" barrel and yet runs about 100 feet per second slower than any .454 revolver I read about in magazines. On the other hand I fired two of my .220 Extremist from the same box of ammo. One was a Savage 26" factory barrel while the other was a 30" Pac-Nor. The 30" was 295 feet per second faster than the 26". This was from the same box of ammo on the range during the same shooting session. I don't believe 4" of barrel made that much difference.

JMR I know what I posted sort of glossed over the issue and the reason it did was because it is very hard to generalize and every barrel has the potential to be "different".

I have built a good many barrels with over sized groove diameter.....say .278 in 270, .285 in 7mm, and others from 300 to 375. Or at least those are what I asked for and assume that's what Krieger gave me. Seems they behaved "looser" and took somewhat heavier charges for the same velocities. Were a tad more forgiving at top end loads.In some cases they went faster than what we are used to seeing but that could have been that I was leaning harder on them(?) In general I always found them less touchy and more forgiving than tighter barrels.

Some button rifles barrels gave more velocity with top end loads than others...there did not seem to be a way to predict it.At least with the equipment that most of us have on hand and you never low whether you are getting more velocity in one than in the other as a result of less resistance to bullet passage, or more pressures , or both.

We had one McGowen 270 barrel...it was a dog and gave 2900 fps with a 130 gr bullet. It did not like to be pushed any harder so we sent it back to Harry and he slugged it at .276. Don't know how he did it but said he lapped it and it came back measuring .2775. Then, it took somewhat greater charges and gave almost 3100 fps with a 130.

My friend and I built two 7mm Mashburns 4-5 years ago. Both barrels were are Kriger #2's CM, 24"....twins. i owned both,ordered at different times. Chambers and throats cut the same,with the same reamer.

His barrel takes about a 1-2 grains more powder,depending on the powder, to get the same velocity as mine.....from the same lots of powder and we tried a few.

WHY? I have no idea.

I have seen Douglas barrels produce more velocity with the same charges, than some cut rifled and Winchester factory barrels....and seen a friends remington barrels show less velocity with the same charges than my winchesters.He noticed this since we shot so much together.

I could cite more examples in everything from 7mm's to 375 H&H but after watching this stuff all these years I no longer worry much about it and take what's on the table from a barrel, fully expecting to see these differences anyway.

In any event trying to get an easy answer to why one barrel goes faster than another is usually traced somehow to max loads and pressures but unless you have a way to measure pressures we are whistling in the wind trying to answer exactly "why".

I do have a hunch, though,that some barrels will show the same velocities at less pressure than some other barrels but really can't prove it...like I said it's a "hunch".

I just remembered I fire lapped my .454. I inspected the bore as carefully as I could as a layman. I carefully loaded thirty cartridges being as fussy as I have ever been by sorting through about one hundred cases. From these I selected the thirty for the test. I fired three five shot groups and then fire lapped it at low velocity with several lead bullets with 500 grit impregnated in them. Then I cleaned it as thoroughly as I could. Inspecting the barrel showed the slightest "chatter" marks in the rifling were gone. I fired the second three five shot groups. They were smaller than the first three and averaged thirty-five feet per second faster. Also the barrel was easier to clean after that.

Ringman there is a probably a reason or logic for this stuff when we se it but for the average hand loader/shooter figuring it all out is a bit daunting.