muzzle jump

chambered221 · Posted: Wed Sep 26, 2007 9:51 am Post subject: muzzle jump

I've been working with a lightweight gun with heavy bullets and a Weatherby mag. Both guns have proven their abilities over the years. What I have noticed is shot strings with alot of vertical. Sometimes pushing the 2 inch mark. I have tracked this problem down to inconsistent muzzle jump. I'm using a traditional tripod rest and rear bag [rabbit ear style] setup.

So my question is, How does evryone else deal with a gun that wants to jump off the front rest?

guncollector · Posted: Wed Sep 26, 2007 1:01 pm Post subject: Re: muzzle jump

if you were shooting offhand or even prone, i have always been told that vertical stringing indicates a problem with breath control. i don't think that is possible with bench rest unless your rests are a bit loose.

one possibility is inconsistent placement of the firearm on the rests - front rest in particular. if the rest is not touching the same part of the forearm for every shot, the POI can vary vertically. Be especially careful not rest the sling swivel on your front rest. I have made that mistake a time or two.

i believe that most, if not all, of the muzzle jump occurs after the bullet leaves the barrel. In fact, the jump along with some of the recoil is the reaction to the bullet leaving the barrel. i don't think the initial explosion of gunpowder way back in the chamber exerts upward force on the muzzle as much as it exerts rearward force on the bolt and, of course, an equal amount of force on the base of the bullet.

FALPhil · Posted: Wed Sep 26, 2007 3:45 pm Post subject: Re: muzzle jump

I have not done the research myself, but I have been told by competitive shooters that lightweight barrels are not consistent when it comes to muzzle whip. There is one load per combination of reloading components that gives you the best group, and when you change one of the components, you get unpredictable results. After all, taming muzzle whip was the whole idea behind the USRAC B.O.S.S. system. It's all in the harmonics.

I do have experience with B.O.S.S. and it works pretty darned good.

chambered221 · Posted: Wed Sep 26, 2007 4:39 pm Post subject: Re: muzzle jump

FALPhil
My concern here is about a gun jumping off the front rest under recoil.
I'm vary aware of muzzle whip and the harmonics in regaurds to barrels. You are right about small changes affecting your results. This paticular gun gave me lots of trouble until I started using a chronograph. It's accuracy comes and goes with 0.5gr changes.
Lightweight barrels tend to be less consistent like you stated but, thats not always true either. Alot of it depends on who is doing the work and how good a barrel is to start with.

guncollector
I do pay attention to the placement of the stock and studs on the rest for the reasons you've stated.
Highspeed photos I've seen with and without porting/muzzle brakes leads me to belive you can influence the bullet in the barrel. Although like you I also belive the bullet is out of the barrel befor the muzzle reaches its peak rise

Vince · Posted: Wed Sep 26, 2007 7:19 pm Post subject: Re: muzzle jump

Hm, this is an interesting one. I'll be following it with keen interest.

Another chance for me to learn something. Woo Hoo

Cheers, Vince

FALPhil · Posted: Wed Sep 26, 2007 8:55 pm Post subject: Re: muzzle jump

chambered221 wrote:

FALPhil
My concern here is about a gun jumping off the front rest under recoil.

My bad. Sorry. Embarassed

The only time I have experienced what you are describing is when I have not had a lot of padding under the forearm and when shooting autoloading milsurps with lots of recoiling mass in the mechanism. I use a sandbag in my front rest that holds about 3.5 - 4 pounds of sand. It absorbs quite a bit of vibration. What are you using in your front rest? Have you tried anything like a Lead Sled?

Deleted_User_2665 · Super Member Joined: May 06, 2006 Posts: 380

Anything "weatherby magnum" is going to jump on a sand bag...regardless of barrel contour.

Felt recoil and barrel vibrations are two different animals, recoil affects "shootability" and barrel vibes affect "accuracy".

Barrel vibes are caused by the initial rapid burning of the powder charge, known to some as the "explosion" contained within the cartridge case........several series of barrel vibes occur before any recoil is at all felt.

Recoil occurs for the same reason the sound of the shot is heard.....all that gas pressure and bullet escaping out the end of a very small tube, though the actual sound is the result of the bullet breaking the sound barrier. "A jet effect" for lack of a better term, is recoil.

A Heavy Hitter bagged on the front just forward of the front action screw will lessen much muzzle jump at the bench.

With bipods, a full backpack supporting the entire underbelly of the rifle will reduce felt recoil from the prone position greatly. Very little muzzle jump as well.

Personally, I NEVER sight in from the bench to hunt. I set turrets from the prone position over a pack with or without bipods, and then confirm other unaided shooting positions and MPAJ during practice.

The bench is for load development.....the rest is Real World.

chambered221 · Posted: Thu Sep 27, 2007 2:24 pm Post subject: Re: muzzle jump

Yes I have a Lead sled and it works great for anyone recoil shy. I use it mostly for my slug guns.

My front rest is a tripod design that uses a Protector owl ear front bag on it. The bag is designed for a tripod rest. It's filled with sand.

Handloader · Posted: Thu Sep 27, 2007 9:18 pm Post subject: Re: muzzle jump

I shoot 416 Rigby and 458 Lott from the bench when working up loads, but, then only with the aid of the Lead Sled. IMO damage can be done to the stock if the sled is overloaded and the stock left to absorb all the recoil. I prefer around 50lbs of lead for this shooting and with it no significant muzzle rise occurs.

Stock design often dictates the direction of recoil energy, whether straight back or at an angle. I have a low comb 375 H&H that jumps completely off the front rabbit ears as, I presume, the recoil energy is directed to a downward angle to the shooter's shoulder which causes a muzzle rise in reaction. High comb rifles, such as my 340 Weatherby, tend to direct the force straight back to the shoulder and seldom leave the front rest eventhough the ftlbs is nearly identical to the 375 H&H.

I believe Windswalker makes a valid point about load development on the bench vs sighting in off a field position. I find some shift in zero when comparing both methods, especially with the heavy hitters and less so with the more moderate cartridges. I believe there is wisdom in checking this out with your hunting rifle and see if this is the case.

Pumpkinslinger · Posted: Thu Sep 27, 2007 11:49 pm Post subject: Re: muzzle jump

I found that, with a hard kicking rifle on a bench, I needed to be aware of holding the fore end down on the bag with the same force every time. I got better groups and didn't have to worry much about "magnum eyebrow".

Jack · Member Joined: Oct 19, 2005 Posts: 98

Try removing the front sling swivel before shooting from a front rest. The front sling swivel catches on the sandbag during the recoil cycle and adds an inconsistency. A front swivel on a sandbag rest is almost a guarantee of vertical stringing.
What you want is for the rifle to slide freely on the bags, the same way every time. Benchrest shooters often use talcum powder, teflon spray, teflon tape, or other stuff to make their rifle slide on the bags with little or no resistance.
Any time I hear 'vertical stringing' from the benchrest, it's almost always a front rest issue, and if you're using a good front rest, and locating the rifle on the rest the same way every time (that's what the front stop is for), I'd bet it's the front swivel.
BTW, the standard QD front swivel is a machine screw that goes into a nut recessed in the front of the stock. Unscrewing the front swivel is usually easy and will do no harm.