Slightly heavy bullet for a given barrel twist?
- Thread starter alpining
- Start date
ultimate_monkey
CGN Ultra frequent flyer
- Location
- victoria BC
only 1 way to find out! alot of the time the stated twist of a barrel isnt EXACTLY what its claimed to be, ocationally you will hear talke about a "fast / slow" (insert twist rate here)
77gn is pushing what a 1:9 will stableize, so you will have to push it pretty fast to get it to work but it is do-able
77gn is pushing what a 1:9 will stableize, so you will have to push it pretty fast to get it to work but it is do-able
- Location
- Somewhere on the Hudson Bay Coast
While I haven't tried the 77 gr MK in a slow twist barrel, I did try the 107 gr 6mm bullet in my 1:10 .243, they didn't work.
Bryan Litz suggests the 77 gr MK in a 1:9 barrel has a nominal stability factor of 1.39, where 1.4 indicates marginal stability; meaning that at sea level with 50% humidity at 59 degrees F, and 2800 fps muzzle velocity. Higher than 1000' of elevation, greater humidity, warmer air, and higher velocity all work in your favor, where for me at sea level with 30% humidity at -30 and 2600 fps velocity in the same barrel they won't work.
Bryan Litz suggests the 77 gr MK in a 1:9 barrel has a nominal stability factor of 1.39, where 1.4 indicates marginal stability; meaning that at sea level with 50% humidity at 59 degrees F, and 2800 fps muzzle velocity. Higher than 1000' of elevation, greater humidity, warmer air, and higher velocity all work in your favor, where for me at sea level with 30% humidity at -30 and 2600 fps velocity in the same barrel they won't work.
You might make them work but you may be right on the edge. At least you're heading the right way in terms of faster twist and heavier bullets. I tried the 77grs in my 22BR and they were barely on the paper at 50 and not one was on the paper at 100 with a slower twist. I'd only load 5 or 10 to start with. Shoot 5 at 50yds and you should know fairly quickly if it's worth trying them at 100.
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
The Sierra 77 Matchking (.224") is a relatively stubby bullet for its weight (it is designed to be able to magazine-fed from an AR-15 magazine).
It is 99%+ likely that they will stabilize just fine in your 1-9" twist.
American bullet manufacturers are exceptionally conservative in their twist estimations. If you enter you bullet's data into one of the enhanced "JBM" ballistics calculated, a stabilty factor >=1.0 indicates that stability is predicted (not guaranteed, but predicted). Anything above Sg=1.10 will almost certainly be stable (meaning: no guarantees, but I'd risk spending $600 on a barrelling job on a calculation of Sg=1.10)
It is 99%+ likely that they will stabilize just fine in your 1-9" twist.
American bullet manufacturers are exceptionally conservative in their twist estimations. If you enter you bullet's data into one of the enhanced "JBM" ballistics calculated, a stabilty factor >=1.0 indicates that stability is predicted (not guaranteed, but predicted). Anything above Sg=1.10 will almost certainly be stable (meaning: no guarantees, but I'd risk spending $600 on a barrelling job on a calculation of Sg=1.10)
Hi folks - Has anyone tried 77gr HPBT SMK in a 9" twist barrel? It says 7" to 8" twist barrels on the box, but I'm guess some of you have tried it...
I am assuming you are talking .223, this is my standard load in my 700P with a 1:9 twist, it shoots well, I have shot it out to 600 yards with no issues
Here is the proof...
