Bedding and Accuracy.

[muffett.2008]

Many years ago, I wrote an article on effects of timber and contact points and the effects on Accuracy.
That article predated these new fangle Computer things.....and is long since lost, those Target Magazines have long since ceased to exist.......pity.

Today on the range, I broke out a 1918 Enfield for a bit of a repeat of the original test, less a couple of tests that were proven to be irrelevant, so here is a shortened version of that original test.......it helps to put some of those weird "my rifle shoots large groups" questions into perspective.

Assuming the rifle is in good/reasonable condition, we check zero as per the original zeroing test at 33yds(100ft.)
Using Reloads instead of Milspec ammunition, I ensure my point of impact coincides with my point of aim, adjusting sights until it does. If this requires changing sight blades, then so be it.

Next test is to apply pressure to the right side of the barrel to simulate wood contact......

Then to apply the pressure to the left side..........
(note the direction with nosecap in place)

The effects of down pressure from the top handguard.........

The effects with no Nosecap ...........

..........and finally without the Forewood...........
(note the high left effect)

The two tests omitted were packing each side of the draws, this had bugger all effect in the past and I doubt that it has any bearing on right or left deflection due to the closeness of these components, a loose forewood jazzing around would be more problematic.

The left of centre without the nosecap in place gives us an indication that the rear bedding is not centred, but in this case it is caused by the left locking lug not making contact.......so this brings that bugbear into play.......even contact is imperative for SAFETY, ACCURACY and reduces excess wear on the firearm.

Looking at the variations per test and doing the necessary calculations, those variations from centre are multiplied threefold out to 100yds.
So if you are only getting a 12" group at 100 instead of 2" then consider the effects of these pressure points as an indication of what could be wrong with your rifle.

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Peter Laidler]

Actual targets like that are a really good idea. I wish we'd had ACTUAL examples like that during our apprenticeship instead of blackboard sketches that we'd discuss for what seems like ages - and ages! A case of one picture, especially a real life picture does describe a thousand words. Thanks Muffer

[henry r]

Thanks. Excellent info.

[jonh172]

Very helpful demonstation, thank you!

[muffett.2008]

Pretty smart bunch we have here Pete, I would have expected the numerous questions we used to get with those blackboard diagrams.
So we all understand the difference between a front bearing barrel and a rear bearing barrel............two words, bend and bow.

[muffett.2008]

It would appear that all was not so clear, going on an email I received today.(not the PM's via this forum, that's ok)
so I will just clarify........if you have sportered your SMLE, than what was posted in reference to shot deviation, does not apply.

If you have removed your nosecap and shortened your forewood, the barrel is basically considered to be floating........or what we call rear bearing, as opposed to the rifle in it's complete form, which is double bearing.

Pressure applied to a rear bearing rifle barrel will deflect the shot to the opposite side, i.e if the barrel is touching on the right side, the shot will go left.
As opposed to a front bearing barrel, which will deflect the shot to the same side as the pressure point i.e right pressure pushes the shot right.
Understanding the bearing points should assist in what actually happens as opposed to what you think should happen.
(This is where that blackboard would be handy Pete)
A SMLE barrel is supported at the rear(same as a conventional rifle) and at the front, by the nosecap. Depending on whether the barrel is light or heavy, it may also have an inner barrel band midway along it's length. Therefore pressure applied to the right of the barrel, actually bows the barrel between the two mounting points, causing the shot to exit to the right, the same side as the pressure point.
Now if fitted with an inner band, the movement is limited to about 1/32", as the inner band is actually loose fitting and normally centred on a correctly setup rifle, this limits the amount of side deflection , but creates a dampening effect at the contact point, causing erratic exit of the projectile due to variations in vibration at a known node.

A heavy barrel does not have the inner band, nor the front spring and plunger that applies upward pressure to the light barrel, pushing it upwards in the nosecap, where it bears on two slight bearing points, ensuring the barrel is always centred on a good unwarped forewood, both the light and heavy barreled rifles are set up with a set amount of pressure at the nosecap, insufficient bearing or no bearing at this point allows the barrel to whip and rounds exit depending on vibration, forming a large hollow group, as opposed to a well fitted nosecap that controls the barrel whip and allows for a much tighter group.( The stiffer heavy barrel is less prone to whip and ultimately easier to control.)

Various methods of bedding or dampening have been employed to try to control this, barrel packing to dampen at select node points, rubber inserts in the nosecap, usually with the barrel free floating, springs to apply pressure to nodes and anti nodes, the list goes on, all covered by marksmen and armourers over the years, however, the most successfull over the years has always been to correctly set up as per the bedding method applied by Service Armourers.

If you have a free floating, single bearing point rifle, action bedding becomes critical, if you have a light whippy barrel...... have fun, if you have a heavy barrel, then add an inch of bedding under the barrel reinforce, ensure your bolt lugs mate, your crown is undamaged and enjoy.

[henry r]

What deviations would happen with an otherwise correctly set up standard barrel if the inner band ot the front spring set up were left out?
Thanks

[Son]

What deviations would happen with an otherwise correctly set up standard barrel if the inner band ot the front spring set up were left out?
Thanks

Without having done the shooting to prove or disprove... It would depend on the condition of the rifle's bedding before the bits were removed.

The inner band and barrel centering stud and spring were originally intended to reduce the effect a warping foreend would have on zero/ accuracy.

From Muffer's info above, you can see what different incorrect pressures did...

If the rifle was set up as intended, as I understand, both the inner band and the barrel centering stud did nothing- so removing them would do nothing.

Conversely, if the foreend had "walked" a little from where it was intended and the inner band and or the barrel centering stud had been brought into play to help dampen effects on the rifle's zero, then removing them would likely cause major movement of POI and possibly accuracy too.

Here's hoping I haven't messed this up....

[30Three]

I found this very interesting. I have a question regarding the possible causes and remedies for a problem I have with my No1 MkIII*.
It shoot's reasonably good groups; a 5 shot group is generally 2 MOA if I do my bit. However when shooting in service rifle competitions; I have found that the group will rise when the rifle is hot. So the second series of 10 shots will be higher than the first series. Obviously with varying time (for target patching) between the series means it's not always the same conditions. But it is a problem as I seem to end up in the white!
Is this a known issue and is there a remedy?
For info; I've been through a lot of work on this rifle to get the groups to spec.( initially it was shooting 12 MOA). It now has a new (old stock) barrel, and I fitted the wood starting from the rear and spending time checking the barrel is centred (it was down the left side originally) and relieving unwanted contact areas in the barrel channel. ( the wood was later BSA manufacture and had not been properly fitted). Also replaced the spring in the front pad and adjusted the nose cap fitting so it just touches the barrel at about 11 and 1 O'clock.bolt contact is even on the lugs. I have kept it stock bedding and have tried to get it right.
Just not sure if I'm missing something.

[Bruce_in_Oz]

Now all we need is a steady and affordable supply of Mk7 ammo and / or components.