I have two rifles that I’m feeding. Both are 308 Winchester. Both are 1:10 twist rate. Both are bolt action. But one of them (mine) has a 26” barrel. The other (my brothers) is an 18” barrel. I’m wondering if more velocity could be gained by using a bit faster powder in the shorter barrel. I’m not talking about chasing a phantom velocity number. Just getting the most from the cartridge in the specific rifle. I’ve found some published loads. I’m thinking like n150(26”)vs N140(18”) or Varget(26”) vs Benchmark(18”)
Barrel Length vs Burn Rate.
- Thread starter JmacD
- Start date
N555
Member
No, slower is faster.
Varminterror
Member
- Joined
- Jul 17, 2016
- Messages
- 14,958
No. This is an old “gun counter fool’s myth,” which truly needs to die.
Faster powders which are slower in long barrels are also slower in short barrels. The ONLY differentiation being that a faster powder - while running slower - may promote less blast and flash at the end of the barrel than a slower powder which is still retaining higher driving pressure at the short muzzle.
But again, faster powders do NOT create higher velocity in shorter barrels than do slower powders.
45/30-06OKIE
Member
Yeah, I tend to think that this is kind of counter intuitive as wouldn't a faster powder have a quicker peak pressure, and thusly, have less pressure overall? IDK, I'm just a grease monkey...
N555
Member
Yeah you would have to go down to like a 7 inch barrel or less before faster power gives faster velocity.
45/30-06OKIE
Member
Ill help you out @JmacD ! I'll load up Gordons Reloading Tool and crunch some numbers for ya!
AJC1
Member
A slower powder provides more gas pressure longer with a longer curve. A short barrel might not take full advantage of that energy resulting in blast and flames... pistols illustrate that phenomenon well.
This is what I was always told and have always done. Had a “gun counter fool” try to tell me that the blast and big flash was “way to much unburnt powder & I better speed it up. So I’m taking from the response(s) so far my misgivings with the “advice” were founded.
45/30-06OKIE
Member
Ok here is a 308 18in 1-10 with a 165gr Hornady BTSP with 44gr of VV N150 (100.1% case fill) notice Powder Burnout is past muzzle, this means it would be very loud and have a nice muzzle flash. Again, out of an 18in barrel.
Here's the same with 44gr VV N-140 (91.0% case fill) instead, however, any more is potentially over pressure according to GRT just fyi. Notice Powder Burnout is at 15in, this means it should be quieter and have reduced muzzle flash compared to N-150.
Edit, "Burnout" doesn't mean unburnt powder necessarily, just that the hot expanding gasses will not be cooled off enough and will make for the big muzzle flash we all love to hate.
Here's the same with 44gr VV N-140 (91.0% case fill) instead, however, any more is potentially over pressure according to GRT just fyi. Notice Powder Burnout is at 15in, this means it should be quieter and have reduced muzzle flash compared to N-150.
Edit, "Burnout" doesn't mean unburnt powder necessarily, just that the hot expanding gasses will not be cooled off enough and will make for the big muzzle flash we all love to hate.
GeoDudeFlorida
Member
- Joined
- Dec 1, 2020
- Messages
- 11,115
In a perfect world the burn is still making expanding gas as the bullet exits the barrel. I try to think about it like the gas is pushing a payload down the tube. The only thing you don’t want is for the payload to start decelerating. That lets friction take over.
My above mentioned misgivings were justified! Haha. That said, my brother’s rifle will really POP. I got spoiled with my 26(when my can comes, might try it on both, though the 8” can will make my rifle measure 56” long… fun to thread through the brush).
Yup gotcha. For what it’s worth, my redneck reloading brain calculator (patent pending hahaha) was about correct at where burnout would be.
Edit: I need to get GRT
Varminterror
Member
- Joined
- Jul 17, 2016
- Messages
- 14,958
Exactly this.
We use slower powders when we have big cases with big expansion ratios and big bullets which take a while to get down barrel - as in 2.21” instead of 1.98”, so we need to retard the pressure spike until the expanded cavity to prevent overpressure. In that same case, a faster powder will spike sooner, meaning to get the same net energy, the pressure must be much higher, naturally, exceeding the maximum pressure standard of the cartridge.
45/30-06OKIE
Member
Yeah It's nice, I played around with it and put in Hodgdon data for a 175gr SMK and Winchester 760 and Ramshot Tac and they were close to each other... As in GRT and Hodgdon agreeing with each other... I would still take GRT with a super small grain of salt though... I would start with N140 in both barrel lengths and see what that acts like and go from there!
Yes. Thank you for filling in the link I knew I was missing!
I will… except I already know mine (26) like N150.
I was using VV app for data start. Lyman 50 has some too.
45/30-06OKIE
Member
Above all else, I would place the most trust and blind faith in the actual manufacture of the powder, so I would use VV's data first unless it was called out in another manual such as Lymans. I noticed their 51st manual seems to have not much variety and only a few bullet types and powder types in it for each caliber... But hey, its another cross reference! LEE needs to come out with a 3rd edition with all the new stuff and expanded powder
selections... I've noticed the LEE manual is weird about powder choice, it will list one grain of bullet in FMJ and then the same grain, in SP, with completely different powders...
AJC1
Member
The rules are a little different with cast, as opteration is an important factor to get right, not so much with jacketed.
AJC1
Member
Lee produces zero data, so I guess it's everyone else's fault.
I can definitely see that.
Hodgdon just put out an email about different bullets etc. I’ll see if I can find it. And get some screenshots.
Better yet:
“Hodgdon Powder Company provides reloading data that covers most bullets available today. However, because there are so many bullet shapes, styles, and construction configurations we cannot create data for every single one. If you cannot find your particular bullet in the reload data there is good news. We provide data in enough variations in most calibers to give you a safe alternative.
Current rifle bullets are constructed with a jacket/lead core or single material (such as all-copper). Bullets with lead cores typically display lower pressures than bullets of all copper or gilding metal structure. As such, we show data for both style bullets in a given weight, as often as possible. For example, should you have a Hornady GMX solid core hunting bullet, but our data for that weight bullet only shows a Speer lead core bullet and a Barnes all copper TSX bullet, use the data for the Barnes bullet. The GMX and TSX bullets being of similar metals and shape, can utilize the same data.
Pistol bullets create the same situation, having even more changes in shape and type. There are lead bullets, copper plated lead bullets, copper-jacketed lead core bullets, and frangible bullets. Frangible bullets are unique such that we always show separate data for them (and recommend not using any other bullet type data).
Lead bullets and copper plated lead bullets yield very similar pressure and velocity results, so when the weights are the same, the same data may be used for each. Jacketed Lead core bullets come in a variety of configurations. Jacketed Hollow points and Jacketed Flat points of the same weight use the same data. Round nosed, lead core, full metal jacketed bullets of the same weight can also use the same data.
In conclusion, bullets with similar shapes and construction materials will utilize the same data. And, above all else, work up your loads by starting with the beginning load and increase charges in small increments, at all times watching for case head pressure signs and stiff extraction.”
Last edited:
45/30-06OKIE
Member
Ahh ha... That makes me feel better about using TTSX data for the CX bullets I loaded for 25-06.
Only difference might be the (if memory serves) extra cannelure if i remember right. And the I believe the CX is a trademark alloy if I recall. But that’s probably exactly what I’d do.
GeoDudeFlorida
Member
- Joined
- Dec 1, 2020
- Messages
- 11,115
I’m not even sure base obturation takes place with slow rifle powder and hard cast bullets. I don’t often recover bullets and don’t recall really looking for or recording any such thing the few times I did so maybe it does take place and I just never noticed. But it seems like the kind of thing that would be noticeable. If that makes sense.
Similar threads
- Locked
- Locked
